I've added some new data to the
stats page. It's an implementation of
Microsoft's TrueSkill.
Basically, it keeps track of two variables—mu, which is your average skill, and sigma which is the uncertainty in your skill. When you play a match, it calculates the change in those two variables based upon the outcome of the match (what place you finished in) and the skills of the other players you played against. The TrueSkill site has a much better explanation, so read that if you're still a little confused.
Note: I did not rig it so I was 1st...

I haven't implemented the decay of your skills over time. I stopped playing with that name, and I guess my ratings were pretty high back then. When I was working on the algorithm the data I used actually had anumeric in 1st place with about 60 points.
In the future I'd like to apply this algorithm to stats from a fortress server. It'd be interesting to see the results.