All things being equal (money, space, etc), would you rather own copies of the books you read? Or borrow them?
I'd rather own the books that I like and love. I like the thought of being able to go back and read them any time I want to. Also, I like looking at books, smelling and touching them (I know, I know), so just to be able to do that all day every day (not that I do *cough*) is a joy to me.
I'm easily pleased.
The books that I don't like, however, I don't really care about, and usually just give away to whomever is interested.