I got a dollar bill in change today, with www.wheresgeorge.com written on it. I had heard about this, so I went to the site and you can track where the bill has been, depending on whether or not the finders log in. It's kind of neat. (Mine had only been in the town I got it from, listed a few days before. Wonder where it will go next - after I spend it, of course). They have a "where's willy" for Canadians.
http://www.wheresgeorge.com/
http://www.wheresgeorge.com/