Book Crossing

The idea behind book crossing is that once you finish a book you should "release it" by leaving it somewhere or donating it, with a code it in and instructions about how to log its movements for the people who find it. I've never particpated, though i did see a book crossing book "in the wild" as they say, but as was a ratty looking Agatha Christie, I wasn't too motivated to take it home. Has anyone actually tried this? The site also has forums where you can chat about the books you read, found ecetera. Please post if you've tried it, I'm curious!