I found an interesting concept linked from Kottke’s remaindered links. The idea is to create an XML-based book list (with the help of an easy-to-use interface), put it on your site and notify this site with your zip code and distance willing to travel. You can then be matched with others in your area, peruse their lists and connect with them to set up a swap. Nice way to trade out some of those dusty books from your shelves. It will definitely need a critical participation mass to be useful, but the seed has been planted.