I know I'm not alone in this, and while I like the smell of a new book, my real kick comes from sticking my nose between the pages of old ones. And that kick stems entirely from the memories they evoke. I have a vague recolection I've posted about this before, although I can't be sure it was here, but old books will remind me of one of two things; and those memories are so vivid I never tire of doing it. Old books will remind me of either the Enid Blyton collections I used to read myself to sleep with as a kid, and if not that, the art cupboard at my infant school, which had a very distinct smell of plasticine, crayons and chalk. I'd be interested to hear if this is what others get from smelling books, or is it simply a pleasant scent that you just happen to like?
Christopher Brosius's perfume house has a scent called "In the Library", based on a specific old book. And the Smithsonian says that old books smell like grass and vanilla: http://www.smithsonianmag.com/smart-news/that-old-book-smell-is-a-mix-of-grass-and-vanilla-710038/
I've just read a few articles on the subject myself, which all seem to be linking the habit to chemical reactions. I eventually found one on Barnes & Noble, though, which confirms I'm not the only one for who the evoking of memories is the prime reason for taking a whiff of that tatty old paperback. http://www.barnesandnoble.com/blog/ask-a-literary-lady-why-do-people-smell-books/