[Kisil]

How about separating "quality" and "agreement" into separate scores?

While it complicates the interface, it would be much more useful for both authors and readers. It naturally leads to measuring controversy - the most interesting comments would be those with high quality and mixed agreement. Having a sense of HN's opinion would direct posts towards areas of maximum contribution. It would also re-direct some of the pile-on upvoting from low quality but obvious/funny/mean/etc. comments, so they could drop down the page despite having some appeal.

Some example cases: a) I may agree with the snarky comment that calls out someone's obvious mistake, but I can simultaneously downvote for snark. b) I may disagree with someone's analysis of the iOS vs Android market battle, but I can now register my disagreement while acknowledging that the poster made a good point. c) I made a comment that came off as means-pirited, though that wasn't my intent. The quality downvotes are an unambiguous message, which I can't just write off with "I guess HN disagrees."

[Kisil]

Side-note: Many users vote, or withhold votes, based on some sense of what the comment "should have scored." Awarding karma only for quality votes allows the reader to register assent/dissent without running up the score. There's a frequent problem where the first comment builds momentum just by being first; this change would at least partially address that problem.