This is the coolest!! BookCrossing.com is a system of "releasing books into the wild" to be read by others, while you track where the book goes. It's like geocaching with books! Too cool!
You join the website (free and private), register a book with an ID number, pass it on by giving it to a friend or leaving it in a book exchange spot (like a laundromat), and the chain is started. If you are lucky enough to find a book with an ID (like finding a geocache!) you go to the website and report your find; then, again, pass it on when you're done.
I love my books but in the RV I don't have room to keep them. With BookCrossing I can "let them go" without really letting them go... I get to see where they are and how they're doing, who they've met -- just like grown kids! I love it!