Implementing the Social Contract in video games

This post is the product of three items, all related: one, a professor who studied online griefing; two, Penny Arcade's Internet Fuckwad Theory; and three, Zero Punctuation's review of Left4Dead.

Griefing is a real problem for all online games; it's the problem of having thousands of people looking for every possible way to try and disrupt other's games. We won't go into the psychology of *that* impeditment, but it's explained by the Penny Arcade Theory. Griefing can seriously impact the customer's satisfaction index with the game, resulting in decreased playtime/interest levels, which results in either cancelled subscriptions or lower sales of DLC/sequels.

The reason that people don't grief in real life is the beauty of the Social Contract. So the question is, how do you implement an Online Social Contract?

I'd be fascinated to hear what the Blizzard folks have learned about group formations in Warcraft, because it's one of the key differences between the online world and the real one. A straightforward approach would be to implement a simple rating system, where other players could judge/rate an individual's actions, resulting in an appropriate reward/punishment system. This fails on several levels. In the online world, it's relatively easy to instantly have several thousand "friends" who will rate blindly. Alternatively, it adds another potential for griefing where people rate others negatively for no reason.

In Left4Dead, which depends on a full 8 players for proper gameplay, the concept of a "ragequit" has quickly emerged. Any player can leave the match (which can take two hours) at any time. This leaves the other players either in a state of limbo, waiting for someone else to join or scrambling to invite friends, or if enough people ragequit (say an entire team), it effectively ends the game. 9 times out of 10, it's easy to tell when someone has ragequit - they're killed, or they spout off before quitting. But sometimes it's not. People's PCs crash, they get a phone call, or Real Life in general takes it's appropriate place in the priority queue.

So starting with a specific situation - how does one implement an anti-ragequit system? or at least one that labels or tags players who have a high ragequit tendency?