A few years ago I had the very half-baked idea of using E2 as a forum for exchanging used books. It kind of worked for a while, but then it got too big, too out of control, and frankly too boring to manage. I am happy to report someone else is doing a much better job with a similar idea.
BookMooch.com is sort of a cross between the ill-fated book lotto and BookCrossing. Like BookCrossing, BookMooch enables you to get rid of unwanted books and pick up interesting "new" ones, and like the book lotto, it lets you choose among titles. And it has gazillions.
What I like best about the site is that reciprocal trades aren't necessary. BookMooch runs on a point system, where points are awarded for building an inventory of books to give away (this means you must first offer books before asking for others), and for mailing those books to other users who request them. Earn a point by mailing user A a book, spend that point by requesting a book from user B. Mailing a book out of your home country earns you more points than usual.
Accumulate more points than you think you'll spend, and the site allows you to donate those extra points to numerous partnered charities, which will benefit a public library or let a sick kid pick out a book to be delivered to his hospital.
There's also an ebay-esque feedback system to keep people honest. I have no idea whether this will work, how tamper-proof the system is, or how many people are using the site solely to scam a few free books. The feeling I've gotten so far is that most people are there primarily to get rid of books (I certainly am - seriously, if you're in need of an anthropological paper on ancient Mayan life, I'm your girl.).
BookMooch is fairly easy to navigate, and buzzing with activity - apparently it's attracted about 3000 new users within the past week. I created an account, posted a few dozen books, and had a request for two within minutes. There are still bugs and minor weirdities, but it's running pretty smoothly considering the site's all of nine days old and is being operated by one guy.
An overview of the site can be found here. Also includes a photo of founder John Buckman wearing a carrot salad.
update: a few interesting stats on the site's tenth day: -
total members: 4056
-
members listing books to give away: 1,566 (38%)
- total books available for mooching: 19,067
- countries participating: 44
Update: Sept 11: I've just received my first three books, in perfect condition. Also I've set up a BookMoochers usergroup (21 members so far), which I don't imagine will see much chatter, but will serve as a useful way to track which E2 users are also BookMooch users. To be added to this usergroup just msg me or XWiz. | 
