If you hover over their karma score, the ratio appears, and the same if you hover over the score for a post or comment. So far as I know, it's a feature which was added recently.
The next frontier would be a chart which showed how the karma ration changed with time.
Oh, that's not what I meant.
I meant something along the lines of (upvotes + downvotes) / (markCommentAsRead hits). Perhaps with some fancy math to compare against voting rates per pageview and zero-vote "dummy views" and other noise factors.
Something to give a rough idea of whether that "4 points" comment is just something four statistical outliers found nice out of a hundred readers who mostly didn't vote on it, or that all four of four other participants in a thread found it useful.
I haven't yet thought through whether I would real...
If it's worth saying, but not worth its own post, even in Discussion, it goes here.