From Dan Abercrombie who runs the site:
The site works by users posting what they have to offer, when someone requests one of their items they send it out. In doing so they receive points that can be spent on anything else on the site. The sender pays the shipping, but the favor is returned when they request something. The site is free, with a few added features for a minimal fee.Check it out, looks like a good way to get rid of books you don't want and to pick up a few new ones!
To give you a little more information about the site, it was opened in September of 2004. A couple months earlier my sister came to me with the idea for a new website. She had a lot of books and a small house and thought it would be a good idea to help get rid of some of them. I put it together in a few weeks and have been working on it since. We have over 180,000 items listed, with almost 8000 users, and 90,000 items have been traded. We're the largest such site that has not only books, but CDs, DVDs, VHS, video games, and magazines. It provides a nice flexibility being able to trade a CD for a DVD for example. The site also supports international trading, users can select which countries they are willing to ship to.