I think to add another dimension--and this could only be done with some greater ability to access data, which I don't think we have (do we, mk?)--is to look at the comment score in the top of a thread, and the number of threads started. The comment score of heavy users is probably driven down by long conversations between users. No one is going to upvote a comment that's the 10th response about some topic that's only interesting to the two parties involved. The number of thread started, and the average score of those initial comments could say a lot about how engaged the user is, as well as how much the user contributes to getting others involved.
Definitely agree with this. There is a lot of data that is just publicly available, but it would just take a long time to organize. In the future, I hope that those who are interested, can organize it all and hopefully offer mk and thenewgreen some useful information to make Hubski even better!