My first trade was Why Bad Things Happen to Good People for Ride the Lightning – I picked up the former, naturally. I followed that up (begrudging full disclosure: the book was for a customer and I have Ride the Lightning on LP) with A Heartbreaking Work of Staggering Genius for Perez-Reverte’s Purity of Blood.
Swaptree’s system is a bunch smoother than any of the others I saw – it only works for books, cds and dvds, and you’re better off staying in the shallow end of the pool esoteric wise, but it’s a nice start. For the others I’ve looked at, it seems like their grasp exceeds their reach – by a lot – they all seem to be shooting for the Ebay of bartering and that’s going to be difficult. The killer app is probably to bring bartering to facebook/cell phones (at least until the lights go out).