We just started Paperback Swap a few weeks ago and we LOVE it! Here's how it works:
You create an account.
You post as many of your books as you are willing to swap with other members on your bookshelf. After you post your first nine books you get 3 FREE credits! These do NOT just have to be paperbacks. They can be hardcovers or even audio books!
When someone requests one of your books, you can download a wrapper that automatically prints out the address of the person who ordered your book. You mail the book, and you pay the postage, because when you order a book form someone else, they pay the postage on the book being shipped to you.
When someone receives one of your books, it is theirs to keep forever and you get a credit which you use to request a book. All books cost one credit each and all audio books cost two credits each. Click on the button to go to the Paperback Swap website! Here  is the sign-up page, and this  is the how to swap books page!
If you sign up, please put my nickname (MaddieLynn) in the referred box. (This will give us an extra credit.)