The problem with average karma is stat it strongly discourages people from posting replies to less popular or older messages. I've made a conscious choice to ignore my average karma. I dont think it is conducive to good conversation, as it tends to be heavily biased towards the first few posts.

I wonder if we should go the other way -- I always liked slashdot's system of a 5 point cap on any post. Is a 500 point post really enter than a 100 point post, or is it more likely it is seen more often?