Karma only gives you one bit of feedback per person voting. A [+] or [-], that's it. We can probably do better. Even so, it's much better than nothing.

I don't have time to read every single comment when there are hundreds to sift through, but I can read the important ones. The only way to find the important ones without reading everything is through karma. For example, SSC posts can get a comparable number of comments, but I've given up reading them.

Adding even a few more bits per person to the signal could improve quality a lot. On the other hand, simplicity is one of the karma system's strong points. The low effort required encourages participation, as you pointed out. I don't want to complicate the system too much, but I don't think the current version is optimal.

We could take an approach similar to Google’s PageRank, so votes by high-karma people carry more weight. This wouldn’t require any more effort for participation than it does now. We could perhaps keep the current one-bit system for determining karma score in the first place, but we would be able to sort posts/comments by the weighted score.

I’m not sure how hard this would be to implement. The database must have enough information to do this, since it tracks who made each vote. I’m also not sure how to set up the weighting function, but this sounds like a job for Bayesian methods—some of us are good at that, right? :)

Getting downvoted can be discouraging. People who get downvoted enough (or fear getting downvoted enough) may not participate. Sometimes this is a good thing (e.g. trolls). But in other cases, there could be people with important things to say, who could improve their quality with just a little guidance.

For anyone reading this, what are your usual reasons for downvoting?

Perhaps they fall into some common patterns we could enumerate. (Perhaps a fallacy or cognitive bias from the sequences?) If so, we could add flags for these common reasons to the comment system. Marking a flag would count as your downvote, but would provide much more valuable feedback to the commenter, and also to other newcomers. We could control these specific problems without discouraging participation as much as a simple “[-]. You’re wrong. About something.”, like we do now.