Our friends at Tricycle will push through a zero-based karma system (no self-voting possible) sometime this evening. At present this will only cover future posts/comments - they may go back and revise history some time in the indefinite future (or not), but apparently that would be overly complicated for now. We'll see how this works.
The rule should be stateless: users vote, and it's data. Then, there's an algorithm that computes karma of users and rating of comments, starting from that data. Giving more weight to high-Karma users (adjusted for inadequate voting=significantly different from what others value, and for balance of votes) is similar to electing moderators, and ultimately roots in the founders' conception of what's on-topic, what's valued on this particular forum.