Is karma for people even useful? Personally I rarely ever look at a person's profile, and if I do, I'll probably click on their "submissions" overview anyway.
Therefore for me, points on messages would be sufficient.
That way it would not be possible to frustrate users by depleting their karma (second time I witness this on news.yc, last time it was juwo).
I've found it relatively useful as feedback. It's sort of fun to see which posts get points, which don't, and which get tased.
If a solution to problem is necessary, I would first suggest scrambling the order of the leader board and hiding the Karma. At least, hide the Karma from the leader board listing itself. That would preserve recognition for the top contributors but there'd be less competition for the #1 spot.
Oh, and I like being able to downmod a post that was stealth-edited after I made a response for the sole purpose of saving face at my expense.
Therefore for me, points on messages would be sufficient.
That way it would not be possible to frustrate users by depleting their karma (second time I witness this on news.yc, last time it was juwo).