Inciteful posts rank lower. Incitefulness being ranked as some function where upvotes increase the score and number of comments decreases it.
Yeah, dang's discussed that in the past. Among other factors for ranking is the comment:upvote ratio. And I think quality of comments and discussion, they have a flamewar detector (speed of replies and depth of comment thread nesting) which can also impact ranking.
I've noticed this place seems to have a really high churn rate. I often find myself replying to comments that are only 5 minutes old. :P