Redditors often argue that karma is make believe number, where in reality it is the most tangible evidence of social influence and worth - essentially karma is a quantification of worth in the reddit community. So I see the key for hubski is equivalently ensuring that popularity ties to the behaviors that you want to promote.
I think there's a danger in making it too much like "goods and services" but I think that allowing people to redeem their hard work for "valuable cash prizes" is a good motivator. Perhaps it's a semantics problem: "karma" is, from a Buddhist perspective, a BAD thing. Perhaps "trust" is a better word. Then the question becomes "how does one earn trust?" I'm sure I'll regret all of this when I sober up.
I agree that having the "hub-wheel" top out is a good thing. It's a way to see that what you're saying or contributing is appreciated. Thats it. It's not a commodity. I think that the one "motivator" that is in place now is how many followers one has. I'm not here for the competition, but if I were that would be one way to know how I'm fairing.
When this was nominated for "comment of the year" in 2009 it had 1800 points: http://www.reddit.com/r/AskReddit/comments/ahg8x/what_is_the... Compare and contrast with yesterday's top comment: http://www.reddit.com/r/AskReddit/comments/lpwv1/reddit_what...
Wonderful stuff. I don't even want to read yesterdays top comment. I will be re-reading your comment later to my wife. It's worth sharing and resharing.