There is a 2011 study making the internet rounds these days and the less scrupulous are saying it shows 50% of Viking warriors were women. The study itself does not draw this conclusion. But it does beg the question whether or not warrior women were more common in these cultures than others at the time. If they were in fact more common, how did this affect gender roles at the time and in the future?
Ok, let me start off by saying that there is absolutely no evidence what so ever that 50% of Viking warriors were women or that a significant part of any war party was ever made up of women. There are isolated events in which we have some indication that women took part in battle but this was often under more or less desperate circumstances.
Weapons are occasionally found in female graves but these are relatively rare and quite possibly ceremonial in purpose. Shieldmaidens are however relatively common in Viking (and proto-germanic) lore and mythology but there is no indication that this reflects a historic basis.
Now to Viking women in general and gender roles. While viking women are often depicted as enjoying a great deal of freedom and independence in fictional accounts, viking society was very much male dominated. A woman was for example subject to her father or husband. She was not allowed to cut her hair short, dress as a man or wield weapons. (Grágás)
Women were not allowed to speak at general assembly (ting), be judges, witnesses or chiefs (yes, despite what is shown in Vikings). As a very rough rule, anything that happened indoors was womens domain, everything that happened outdoors was the responsibility of the men.
Gender roles were fairly rigid in norse society. Women were expected to handle primarily domestic duties. Women did not trade or raid, nor were men expected to preform female duties. The real big "if and but" here is that widows had a whole different situation. A widow basically inhereted everything, even positions of power in some cases. Widows could become quite wealthy and powerful.
Norse society showed relatively little tolerance towards violence or unwanted attention towards women. Even something relatively minor, such as kissing a woman against her will, could result in the man being fined (Kormáks saga). Even in battle or "attacks on a household" women and children were generally allowed to leave. To injure or kill a woman or child, even accidentally, was considered dishonoring (do note that this only applied to viking women and children).
Compared to the rest of Europe at the time, Viking women enjoyed a relatively large degree of freedom but it was still far from an equal society.
It's been doing the rounds since at least early September, and here were the responses given then, including my own. Well worth checking out are these links which are also contemporary (and while linked in the response are worth posting here).
These are two highly detailed academic blogs by one of the most widely respected early medieval historians currently living. This is, of course, Guy Halsall of the University of York.
http://600transformer.blogspot.co.uk/2014/09/the-viking-presence-in-england-burial.html
http://600transformer.blogspot.co.uk/2014/09/warrior-women-more-thoughts-on-alleged.html
Another interesting, if less academic, insight is provided here.