One of my readers, Tide, has developed an application with which to track the reputation of a player, named Playerep. (No idea why they spell that with only one "r") The application is in the beta version, but they just developed a World of Warcraft addon to use the service from inside the game. The idea is to judge other players on scores like competence or fairness, so that you can easily identify good players to group with.
Of course the problem is that the other player does need to be a Playerep member, and thus the service will only become useful when many more people sign up. Other WoW addons like GEM or other group-finding tools suffer from a similar problem. In the case of a reputation tracking utility, it is likely that the griefers simply won't sign up.
Well, have a look at it. Maybe this is the next big thing in MMORPGs.