At first it bothered me that I could make a comment on something, maybe not a comment that everyone would agree with, but a comment that I believed, and yet I'd be down-voted. I'd watch my karma tick away and be like "What are these folks doing? What on earth is wrong with what I said? How does it lessen the quality of the conversation?"

Then I realized, it just doesn't matter. This isn't a contest, it's a community. All this measures is the general vibe of the comment. Higher numbers = better vibe. A fuzzy value at best.

More useful I think would be to see the total score, but also be able to mouse over the score to see how many down-votes and how many up-votes something received. But that would very likely require a big change by PG to maintain three scores, not one.