zlacker

Base moderation on a points system, a la Slashdot. Grant a user one (or three or 6.5 or n) mod point every time another user replies to one of his comments.

The effect this has is twofold. It grants some incentive to posters who start comment threads, rather than making just single comments which are likely to strike more users' upvote chords. It also reduces the tendency to blindly upvote or downvote based on agreement or for dumb humor.