I'm not sure I agree with you. Karma as a measure of personal worth is silly, but as a way of cutting down on trolls it works pretty well. That number at the top of the screen is something that I'd bet the Reddit and TechCrunch commentors would care deeply about, and as such, it keeps them from dumbing down the discussion here too much.

In any case, HN is by far the best self-moderated discussion forum I've ever seen, and I'd be leery of making any major change that might conceivably disrupt that.