SlashDot uses a point system called "karma" as a way of rewarding contributors to their site. When you add a comment to a story authenticated users can rank your contribution on a scale of 1 to. The more positive rankings you recieve the more karma the system awards you. You can spend your accumulated karma by posting comments at an artifically bosted ranking.
Anyway it's worked pretty well but there have been people who have figured out how to work the system and get the most karma for the least work. They are called a KarmaWhore by the rest of the community.