Wow, I must say some of you guys are up-tight about your books, but I like it, though. I respect people that are careful with their stuff. The only thing I'm careful about is to eat around the book, and I always wash my hands before touching a book.
I never fold the corner of the pages, because, I don't know, but I just never have. But I do fold the pages, and I do make lines on the spine of my paperbacks. I've never been too careful about the condition of my books, as long as I keep them readable.
And for the disrespecting the author-part, feh, I think they feel respected as long as you buy the book. I guess they would have been more offended by people borrowing from a library, or buying old copies from a garagesale. If you catch my drift.
I love my books, I carry them around. They are bound to get small damages. I'm just making them mine. I sometimes make notes in the margin too.