> Maybe if people knew that their reputation and voting influence are on the line, they would try harder to write more constructive comments. Thats all speculation of course and the only way to find out is to experiment :)

You could ask folks first. Not as reliable, but a lot less expensive.

Here's an unsolicited data point. I've got reasonable karma. I don't care about karma. And, I'm pretty sure that the some of the most interesting folks don't care either.

That's not quite true. I do care about all the karma whinging. I dislike it.