TL;DR: (probably much) less common than generally assumed, and mainly limited to the middle to the upper strata in the society.
In order to answer OP's question, I'll illustrate three relevant information of the Vikings and the basic society structure in their homeland, Scandinavia below at first.
The relevant questions are namely:
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1. How many people usually got on a single Viking war ship?
It is relatively well-known that the specialization of the ships (together with the introduction of a sail) occurred in the beginning of what we call the Viking Age (ca. 800-1050), in the 8th or 9th century. The Scandinavians in the Viking Age already used different types of vessels like faering, a small boat for fishing, much larger knarr, mainly for trading or settlement to the new land, and further, the the most renowned one, longship mainly for the expedition or the naval warfare (Cf. Nordeide & Edwards 2019: 28). Of these three main types of the vessel, it was the longship that only really fit well with the purpose of plundering expedition, for its swiftness as well as shallow water draft. It was indeed an important secret of the Vikings to their success.
As I once wrote in the question thread, How large would Viking raiding parties be?, this longship (war ship) usually had 15 (16) to 20, and further to 24 oar benches on both sides. While the maximum capacity of the crews (sailors and warriors together) exceeded 100, the usual number of the crews would be rather smaller: To give an example, the latest introductory book by Nordeide and Edwards suggests ca. 65 to 70 per a single Viking (war) ship (Nordeide & Edwards 2019: 29).
Then, the next problem arises. How were the crews of such a large Viking ships gathered? Was it like a ferryboat in which the passenger Norsemen just rode together for the wealth? Some Icelandic sagas might give such a impression, but we should now take the ownership of the longship into consideration.
2. Who had/ own the ship, especially a longship specialized in the battle, in Viking Age Scandinavia?
Later law books in all the three Scandinavian countries from the high middle ages stipulate that large-scale royal naval conscription system, called leiðangr. According to these stipulation, free (in a legal sense) farmers in each district were required to provide with men, some weapons as well as armory, and further, a ship with sailing equipment in response to the royal summoning of the fleet. They also had to maintain such a district's ship with equipment under penalty of fines. A royal biography of Norwegian Kings dates the origin of such a royal naval conscription in the middle of the 10th century, but, as we will come back later, recent scholars tend to disregard this later account as a literal evidence of kingdom-wide leiðangr, at least not as is stipulated in the extant manuscript of the lawbooks).
A small number runic inscriptions indeed testifies such a joint ownership of the ship in Viking Age Scandinavia (Cf. Jesch 2000: 180ff.). The runic stone U 778 specifies that the dead son of the erector, Baggi, 'who alone owned a ship', but this wording presupposes another type of the ownership, as is shown in DR 66: 'Gunnulfr and Eygautr/Auðgautr and Áslakr and Hrólfr raised this stone in memory of Fúl, their partner, who died when kings fought' (Both English translations are taken from the linked sites). Some scholars interpret : fela(k)a : sin, translated here as 'partner', in a legal sense of joint-owner of the ship as well as a companion of the expedition (Jesch 2000: 180). My knowledge on this kind of runic evidences are at most less than satisfactory, so /u/Platypuskeeper must know more about this topic (as well as the expedition of Yngvar to the East as a background of U 778 runic inscription).
Thus, both sole and joint ownership of the (war) ship were possible and can be found in Viking Age Scandinavia.
3. What percentage of the population could really involve the ship ownership in Viking Age Scandinavia?
Viking Age Scandinavia had a slavery, and one assume that the thralls, or such legally un-free people constituted ca. 20% to 35% of the total population in the later phase of Viking Age (Cf. Jón Viðar Sigurðsson 2008: 20). While there was considerable degree of being unfree among such people from a social point of view, I suppose that they couldn't usually own ship solely or involved with the joint ownership, so we can exclude them with relative ease from our discussion here.
A possibility of the female ship ownership might be very interesting question, but AFAIK we have no positive evidence of such female ship joint-owner so far. It means that the crews of the Viking ship were primarily limited to free male member of the society.
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Here it is time to turn our attention back again to the basic organization principle of the Vikings. The text of aforementioned runic inscription, U778 states as following: 'Thjalfi and Holmlaug had all of these stones raised in memory of Banki/Baggi, their son, who alone owned a ship and steered to the east in Ingvarr's retinue. May God help Banki's/Baggi's spirit.....' Even if the Baggi (Bakki) was a sole owner of his own ship, but he could surely neither sail the ship by himself nor fight by himself. What the text of U778 also presupposed is the (military) retinue of the local chieftain, Baggi.
According to Niels Lund, an expert of the military system of the Viking and Medieval Scadinavia, the fleet of the Vikings from the 9th to 11th century was primarily a scratch team of retinue (lið)s of various chieftains, though sometimes under the strong leaderships of capable rulers like Sweyn Forkbeard or Cnut the Great of the Danes (Lund 1993), as Baggi joined the expedition under the leadership of Yngvar together with his retinue. There are ca. 20 known runic inscriptions in now Sweden that commemorate the dead members of this Yngvar expedition to the East (now Georgia?), and the number suggests that not a small numbers of local chieftains like Baggi joined the fleet.
As for your last question (the commoner's view to the Vikings at that time), I cannot answer with certainty, sorry. It should be emphasized here, however, that our extant evidences almost without exception came from the upper strata of the society, at least in the local level. Neither Baggi nor his parent who made U 778 inscription raised in 11th century middle Sweden were ordinary farmers. Not all the Scandinavians in the Viking Age afforded to commission either a rune stone or a poem of war, or to own a longship. In a strict sense, the majority of the well-known warrior culture ethos of the Viking Age Scandinavia in fact belonged to them, the warrior elites of chieftains and rulers, though I'm not sure whether other people had any right to say to such characteristics or we had any access to their view of society in Viking Age Scandinavia.
References:
This is a question impossible to answer with any certitude. The modern fascination with statistics dates only to the 1700s or so, and rigorous accounting of populations and occupations began much more recently. That said, we can make some cautious estimates.
Regarding the overall populations of the Viking Age, I think our best point of reference is the Domesday Book. This was basically a tax assessment conducted for William the Conqueror of all his holdings in England in 1086. It has its own problems. There was no standard census form, and it seems like different agents showed differing degrees of rigor and accounted for different demographics in different ways. For example, the agents sometimes counted individuals and sometimes they counted households; sometimes their methods for counting varied based on the class of people that they were counting. Nonetheless, their reports are the closest thing we have to a modern census for the Middle Ages and dates from just after the Viking Age.
The numbers of the Domesday Book can be extrapolated in various ways to estimate the overall population of William's England in 1086. These figures yield a plausible population of perhaps 2 million. That's only 3.7% of the present-day population of England at 55.6 million. Lots of things have helped in this increase, especially the extension of arable land (e.g. draining the Fenlands), the establishment of global networks of food supply (thanks Canada!), and the dramatic growth of urban centers, particularly London.
We might assume that similar processes happened in Scandinavia, perhaps yielding a similar change. I've played with the numbers a bit, for example taking into account changes in arable land, and I've landed upon estimates for a Scandinavian population (modern Norway, Sweden, and Denmark) of roughly 700,000–1,000,000. I don't doubt that there are errors in these methods, but I do doubt that greater precision is possible.
The most important thing is the magnitude of this estimate, pointing to a population under a million and likely with wide fluctuations based on climate change (yes, it was happening then, though humans were less of a factor), the rise of deep sea fishing, the intensification of agriculture corresponding in part with the arrival of church landownership, and the emigration of perhaps 30,000 souls to Iceland.
Estimating the size of viking armies is just as difficult. Our textual sources are problematic, since medieval writers used numbers to gesture at scale and sometimes biblical parallels (using numbers like 7, 12, and 144) rather than to represent precise counts. The Anglo-Saxon Chronicle, for example, was written in the 890s, and its author basically indicated three stages of escalating viking activity: (1) three ships arrived in 789, (2) 35 ships in 836, and (3) 350 ships in 851. These numbers look suspicious, even if you don't know much about how medieval writers used their "statistics" loosely.
These statistics nonetheless give grounds for making an estimate of the size of a viking army. We have a handful of Viking-Age ships, surviving predominantly from early-Viking Age burials in Norway and a late-Viking Age harbor defense at Roskilde in Denmark. The biggest of these ships could boast a crew of 80 men, but a more modest longship might sail with a crew of about 30.
If we generously assume that viking crews averaged 60 men and that viking armies drew from the crews of 300 ships, we'd arrive at an estimate of 18,000 men in a viking army. Such populations were unheard of in the Viking Age. Large Scandinavian settlements like Kaupang, Hedeby, and Birka—based on their land area—probably never numbered more than 10,000 residents, and 6,000 seems a more reasonable number. Sustaining 18,000 warriors abroad would take an intensive amount of support, typically seen only in the contexts of modern nation-states. To give a modern point of comparison, a US Marine division typically musters about 20,000 marines, and each division requires about 40,000 marines serving in support roles.
Further problems arise when we start to think about the land area occupied by Viking-Age armies. At present, the smallest base to host a US Marine division extends over 70 sq mi (182 sq km). In 855, a viking army stayed through the winter on the Isle of Sheppey near the mouth of the Thames, making do with no more than 36 sq mi (93 sq km). In 872, a reportedly larger army overwintered at Torksey, occupying in a compact area of 0.2 sq mi (0.55 sq km). In 873, the same army, or perhaps a part of it, overwintered at Repton, building a defensive perimeter that enclosed only 0.001 sq mi (0.004 sq km). At 50,000 sq ft (4,600 sq m) that's roughly the size of ten small apartments!
The work at Torksey is the most recent, and researchers there have calculated that the site could have plausibly supported about 1,500–5,000 vikings. This was the Viking Age at its height, and other warbands were being documented in Ireland and Francia, while archaeological evidence suggests further groups might have been active in Scotland as well.
All this evidence gives us a minimum (based on the Torksey estimates) of perhaps 6,000 vikings and a maximum (based on the Anglo-Saxon Chronicle) of perhaps 72,000 vikings. Within this range, based on my own familiarity with the archaeological and textual evidence, I think we might plausibly arrive at an estimate by taking the high Torksey number (5,000) and assuming that the vikings in England represented about a quarter of all vikings in Western Europe, for a total of about 20,000 active vikings.
Given our earlier estimates of the Scandinavian population at 700,000–1,000,000, that means somewhere between 2 and 3 percent of the population was raiding abroad. I would tend toward the lower side of this number, since not all vikings came from Scandinavia. Some were recruited at home, like King Alfred's usurper nephew Æthelwold, and others were recruited from further afield, such as some who were captured and executed in Dorset at Ridgeway. The Ridgeway vikings are especially interesting since scientists discovered that they typically started eating more fish later in life, apparently once they joined a viking crew. Some of these vikings of distant origins might in fact have been slaves, given that later Scandinavian law forbid letting slaves make up more than 10% of a crew. This all points to diverse social origins but a degree of experiential leavening that came with joining (or being forced to join) a viking crew.
These are only rough estimates, but I think they have some interesting implications, again taking modern comparisons into account. At present, the US counts some 20 million veterans, making up about 7% of the total population. By this rough (and problematic) measure, the modern-day US is actually a much more militaristic society than Viking-Age Scandinavia.
It's easy to play with these numbers (both Viking-Age and modern day) in either direction to manipulate comparisons. That's not the point. Instead, I hope only to point out that this question about the Scandinavian involvement in viking activity—and it's comparability to modern US involvement in its military exploits—can get us to question some of our longstanding assumptions about the Viking Age (and our answers to the latter parts of your question must inevitably be based on such assumptions).
If the numbers abroad were small—only 2 or 3 percent—were these really the spear-shaking militaristic people that later Norse mythology made them out to be? Conversely, even if viking armies were a small part of the overall population, given that about half of the modern US budget is earmarked for defense, how deeply did viking logistical demands shape the rest of Scandinavian society?
At any rate, as problematic as it is to make statistical estimates about the past, I think that doing so helps us think more critically about the past and ask better informed questions. This was a good one!