I think it's interesting. I said "hmmm" when I read the suggestion. But, I'm a pessimist by nature, so in addition to the foregoing critiques from other users...
Understanding that high forum participation by as many users as possible is something we want (or at least I want), I tend to think some people would be put off posting in the forums because they would be concerned that they may receive a negative forum rating. Further, if someone received a lot of negative forum ratings (without doing so purposefully, which no doubt some would do), they may not post in the forums again.