The VW's The Fun Theory is an effort built around the idea that you can use fun to change people's behaviors. They try to prove this theory through a contest where people submit their social behavioral experiments in fun. You would probably recognize some of the entries (such as the piano stairs).
In enjoyed the latest winner, The Speed Camera Lottery, by Kevin Richardson. This experiment tries to get drivers to obey the speed limit for fun, by turning a speed camera into a lottery machine. The speed camera takes pictures of people who speed, in order fine them, and pictures of people who follow the speed limit, in order to give them some of the money collected from the speeders in the form of a lottery. The results are pretty impressive.