I hope this kind of question is allowed on this subreddit. Feel free to remove it in case it's not.
I'm just curious about the quantity of information that an average historian would sift through during the course of a year. How many book do you read? Do you read them all carefully or do you skim? Do you have a special way of taking notes? How often do you read books about a different historical period?
My amazon orders suggest I went through about 180 books last year.
Full reading? Not most of them - information is often repeated, so you're looking for either very specific information, or particular arguments. I'm almost incapable of full reading anymore, but I've sped-read since I was a child which hasn't helped.
Notes are done in Zotero and Freemind.
I generally read anything that interests me, but I'm probably about 50-70% in my main interest areas.
Well let's see, in the past year I have read at least over 3/4ths of (like said by Flubb, some things are repeated and you can just brush through them):
Swords Around a Throne by John Elting
The Marne, 1914: The Opening of World War I by Holger Herwig
The First World War: Germany and Austria-Hungary 1914-1918 by Holger Herwig
The Mathematical Universe: An Alphabetical Journey Through the Great Proofs, Problems, and Personalities by William Dunham
On War by Carl von Clausewitz
Tommy: The British Soldier on the Western Front by Richard Holmes
Pyrrhic Victory: French Strategy and Operations in the Great War by Robert Doughtry
Wars of German Unification 1864 - 1871 by William Carr
Hot Blood and Cold Steel: Life and Death in the Trenches of the First World War by Andy Simpson
The First World War by Hew Strachan
The First World War: To Arms: Volume I by Hew Strachan
The Campaigns of Napoleon: Volume I by David Chandler
What I've still got a way to go with / what I'm procrastinating on:
Napoleon's Great Adversary: Archduke Charles and the Austrian Army 1792-1814 by Gunther Rothenberg
Engineering the Revolution: Arms and Enlightenment in France, 1763-1815 by Ken Adler
The First Day on the Somme by Martin Middlebrook
The Kaisers Battle by Martin Middlebrook
I'm basically hitting that wall that Flubb may be describing if I'm not wrong, that is, most history books out there that are more generalized and open and cost reasonable prices are just repetitive. I need those David Chandler books that cost $150 new and $80 used and give stupidly in depth information to learn anything meaningful. So I'm certainly slowing down but I'm trying to have at least 2 books I'm reading at all times as that's basically the pace I've been running since the start.
As you can see I've read precisely one book outside of my area of interest and that was the math book, but I do intend on branching out a bit more in the coming year because of the aforementioned issue. Considering breaking into the American Civil War for instance but I'm more keen on getting into the social history of the events I study as well.
If the book is on my iPad I just use the kindle app which lets me highlight notes like 4 different colors so that's helpful. If it's a physical book I actually have a bit of a habit where once I'm done reading I'll write out a 1-2 page essay kind of explaining what I read and making some conclusions. Your teachers had it right -- writing papers and stuff really helps solidify concepts into your head and even if I'm not taking a class on the book I still like to use the strategies from a class in helping me learn it. I know it's dorky but eh :P
Followup: how much of your reading is books and how much of it is journals?
The only piece of individual research I've done is my undergraduate thesis. I only really worked on it for one term, but I still cited around 25 books and 10 articles (with another 10 or so primary sources). There was also another 15-20 books that I read/partially looked through to develop my understanding of the topic that I didn't put on the bibliography. Overall, I probably only read 3 books cover-to-cover though - I felt that as long as I read the relevant parts of a book, it wasn't necessary to read the same material again and again.
More generally, my history degree was quite intense, so I always got a 2-3 pages long reading list for an essay every week (sometimes more...), but no-one I know ever read that much or thinks that it's humanly possible - skimming through a handful of books and a few journal articles is generally enough.
I read about 5-10 book per class, as well as a few articles, as a minimum for each graduate class. Working on papers and a thesis adds much more to that. A graduate student in history could easily go through 100 books in a year.
Then again, you are rarely reading a whole book cover to cover. There just isn't time. Skimming and looking for pertinent information are key. Sometimes you are just reading one chapter, other times skimming for supporting information, and occasionally 'reading' the whole thing for a presentation. I take notes on the fly on my tablet with an attached keyboard.
Any reading about a different period is pure reading for pleasure, and I get through 3-5 of those a year. It takes me a while because I have to put them down often. Like /u/Flubb I like to own the books I read, but it can get pricey.