is a site where you can effectively trade in your books for new ones. You list books you're willing to give away. If someone requests one of your books, you mail the book to them and get one point. You can then use that point to request a book from someone else on the site. (You also get 1/10th of a point for each book you list and 1/10th of a point for acknowledging the receipt of a book that someone sent to you.)
The site is based in California but serves an international audience. You have the option of only shipping to your own country, shipping worldwide or requiring international moochers to send you a request to see if you'll ship to their country, which allows you to check the price before agreeing. If you do ship to another country, you get triple points. (I just sent a copy of Ender's Game to someone in Malaysia. It cost slightly over $5 (a little over double what I normally pay to ship in the US) but I got three points and three books of my choice for $5 is still a pretty good deal.
The only cost is the shipping of books you send out which is typically less than $2.50 for a standard paperback. The site itself is completely non-commercial. They don't even run advertisements, which is pretty impressive considering they facilitated over 600,000 exchanges last year and are on track to break a million in 2010. (The site does accept donations but they're completely non-intrusive about it, placing a link at the end of the navigation links on the main page.)
I've been using the site casually since January and so far I've sent out twelve books and received (or am in the process of receiving) eleven. Two of the books I mooched were ones that I had been wanting to read for quite some time but hadn't gotten around to picking up, two were recommended by a "if you liked this, try this" site so I don't know much about them and the others were all books by authors I've enjoyed in the past and wanted to read more of their work (Nicholson Baker & Chaim Potok, primarily.) Most of the books I've sent out were either ones I didn't enjoy or simply knew I wouldn't end up reading again. (In the case of Ender's Game, it was a large trade paperback and I prefer the small mass market size.)
I pick up a majority of my books from the local used bookstore (usually $2 to $4/book) or from Good Will (50 cents for paperbacks) but I've found BookMooch to be an excellent resource for locating specific books. (If I want a book badly enough to purchase it, I usually use Book Finder
which is a meta-search engine that searches pretty much every site on the 'net that sells books. I've found a whole lot of books on there for $4 shipped.)
Anywayz, I just thought I'd mention this excellent resource for the few people out there who still read.
TL;DR - Move along, this is of no use to you anyway.