Have you seen PaperbackSwap.com? I actually came across it on Ravelry because they have a group. It's pretty cool, and I received my first book today! If you have piles of books around and don't know what to do with them, here's an option. Load your titles-it's easy, you just enter the ISBN-and start swapping. I had two requests w/in the first 5 days.
Check it out.