What an interesting idea. The concept behind BookCrossing is that you leave a book you've read in some location. In it, you write its BookCrossing code. Then, you check the site occasionally to see who picked up the book. And you get to track it as it continues on its journey.
This is an international thing. The three biggest user countries are:
1. USA with 14,628 books "in the wild" currently
2. Germany with 6,938
3. UK with 5,068
In the US, the best states for locating these books "in the wild" are California, Colorado, and Washington.
For anyone in Columbus, Ohio, you've currently got 119 books "in the wild". Hmmm, it seems rather rude to release these to Half Price Books where you both make money from taking them there and force the receiver to have to buy the book - at least one of the Columbus people has done this.
Interesting concept. Sadly, no one in my city has participated. Surprise surprise, given that our biggest bookstore is Waldenbooks in the mall.
[Thanks to Brian for mentioning this in a recent post.]