What's On My Bookshelf Book-Swapping Service

Stumbled upon a great website called What's On My Bookshelf. I think I found it through Digg.com. It's an amazing concept and very similar to the kind of thing that goes on in RoIO (Recording of Illegitimate Origins) groups. You offer up books that you have and want to get rid of and others do the same. You pay when you ship a book, not when you receive, but you have to ship books in order to receive more books. The more you ship (or the more expensive the books you ship) the more you can receive. Everyone starts off with 1 point. I already added three books to my bookshelf (all of which were duplicates after I got married and my wife and I merged out book collections). Each book counted for 1 point so I had 4 points. I then requested 3 books from other people and I am waiting patiently to receive them. No one has requested my books yet although I am sure someone will eventually and I will have to ship them.