At the beginning of every school year, I used to get terribly nervous and didn't really know how to makes friends, so I would literally always have a book on me. I would read whenever the teacher was talking, when we were supposed to be doing school work, yada yada. I always just tore a piece of paper out of my notebook to use. But even that wasn't enough, I had to actually write 'Book Mark' on my piece of paper, and I usually doodled on it too.
I never ever dog-ear my books. I do have a habit of breaking the spines on the paper backs though. Because I usually just flip them over, and they don't want to stay down, so I bend the spine and make it stay. I'd never ever do that to my hardback books though.
I highlight the heck out of my textbooks though, and I have various post-it notes all through them. While my index is pretty good, it's easier just to flip the page with a post it note and find the highlighted section than search my index. I keep all my textbooks too. Cause yeah, no one would buy them with all my highlightedness.
I apparently really like the word 'though'.