Variable Rewards

How might this apply to the Web?

Whether to encourage positive behaviors or to reward someone for simply logging in, what can you give out at random intervals? Rewards can be praise, virtual goods, redeemable points and so on—but without a predictable pattern. When many people are gathered in a highly social context for a short period of time (such as a fundraiser), motivate people to contribute by rewarding randomly selected individuals within the larger group.