This goes along with my last post, about considering books as a "treasure."
Once you think of books that way, you can't help but have a certain reverence for them and this in turn reinforces the idea that they contain something valuable. Accordingly, I don't allow books on the floor, or to be thrown or stepped on. That's just not cool in our house.
Understandably, books get torn and damaged through everyday use - that's different. When they do get banged up, they're repaired as soon as possible. I don't make anyone feel bad about accidentally damaging a book, because if you feel you have to pussy-foot around books you'll be afraid to open them.
But really, you don't step on a treasure chest - you open it. And you savour the treasure.
How did I get my son to treat his books kindly? When I walk in his room and there's a book on the floor, I gasp. I say, "There's a book on the floor!" as if I just can't believe it. (And I kind of can't.) He got the message early on, and now he doesn't like to see a book mistreated either.