While I do respect books (obviously), I am not one of these people who treats their books as if they are still in the shop. I like my books to look like they have been read, and the slightly-worn-ness just adds to their charm, reflecting how much they are loved. I am in no way advocating dropping books in baths or pools (although I have done both, I am ashamed to admit), or throwing them about the room etc.
But I do fold the corners of pages down to save my place. Bookmarks are so fussy, and always fall out and lose your place. They are a very nice item in theory, but not practical enough for me. I also keep the page I’m reading by putting books face down on some surface, which I know is bad for their spines. The whole point of books is to be read, not to sit there looking immaculate.
I think the reason I feel this way is that most of the books I read are either second hand or from libraries, so have already been handled by multiple readers. I like that as well, knowing that the very book you’re reading has been read and enjoyed by so many others before you; it adds a bit of history.
Having said that, I do have a thing for penguin classics. They are so beautiful, they really demand to be kept in mint condition and displayed proudly.