[ComputerGuru]

3) Limiting the visibility of posts based on post quality. The more you post in a week and the lower your per-post average karma, the less an upvote counts. Effective Upvote Value = (per-post average karma) / (posts this week)

You probably weren't around for it, but HN experimented with something like this where each commenter's running average point tally for the last X posts or Y time was visible on their profile and indirectly visible on each of their comments. Their name (comment?) would appear in a different (darker?) shade the higher their running average.

I personally liked it, but it was rolled back after a couple of months. I think people became afraid to make replies that wouldn't accumulate up votes, and I know I wouldn't reply to threads if someone commented a day later because "it wasn't worth it."