Interesting article by Richard Thaler on encouraging good citizenship by making the desired behavior more fun:
Lotteries are just one way to provide positive reinforcement. Their power comes from the fact that the chance of winning the prize is overvalued. Of course you can simply pay people for doing the right thing, but if the payment is small, it could well backfire. …
An alternative to lotteries is a frequent-flyer-type reward program, where the points can be redeemed for something fun. A free goodie can be a better inducement than cash since it offers that rarest of commodities, a guilt-free pleasure. This sort of reward system has been successfully used in England to encourage recycling. In the Royal Borough of Windsor and Maidenhead outside of London, citizens could sign up for a rewards program in which they earned points depending on the weight of the material they recycled. The points were good for discounts at merchants in the area. Recycling increased by 35 percent.