Making things that are fun

A while ago I wrote about making things that are magical. I think fun is also magical. You can make many things fun by changing the incentive structure just a little. Take speed limits for example:

By adding a lottery system, following the speed limit does pay off. But do they work? It seems so:

These videos get me excited about other areas where I could add fun to make myself and others better. How about a game system to keep my apartment clean? Or making public transportation more fun? Foursquare seems to have nailed a incentive system to help people explore their cities and get out more. I look forward to see what they do next. What can you inject fun into?