Sacrilege! There are two types of people in this world - those who use a bookmark, and monsters.
I have had a life-long love affair with books and I develop a tic in my eyelid (okay, not literally, but I do have to bite my lip) when I see that others don't worship the written word as I do. In my defence, I'm all things bookish - apart from being an avid reader, I'm also an author, editor, and proof reader. I stopped lending books out a few years ago (I have, um, quite a few...) because I either didn't get them back, or they came back as others have said - dirty and dog-eared. I love seeing that books have been read, but there's a difference between well-thumbed and not looked after.
If you lend clothes to someone, you'd expect them back having at least been washed - why is the same respect not given when a book is borrowed?
Bookish, run like the wind when she asks to borrow another