I don't quite get what the average karma rating is...is it simply karma-per-post? Because I've seen it jump up and down (on my own account) no matter what I've posted or how little of new karma I may have gotten.
I think it's something like the average of the last 50 to last 5 comments you've made. Maybe with some outliers removed as well.
The main point is that it's not instant (i.e. your last comments are not taken into account) and it uses only recent comments, rather than over the life of your account.
