Interesting concept. Here you can swap your old books for another. Think of it like a book trading system and they do have a ton of listings of books for you to choose from. I mean, surely you don't intend to read and re-read one book right? Might as well hare with others and get books you never read before in return. It is a good deal actually. All you have to do is to mail the book to another and you get to choose from Paperback Swap's nearly 5 million titles. And it is not just paperbacks, you can trade hardcovers, audio books and even textbooks. I know I have tons of such books on my shelf, just collecting dust. Make your books even more useful by sharing them!