As sxjy (or xZerox should I say) stated, once you hit the negatives, you cannot upfame or downfame anymore. I believe we shouldn't have to lose that power, especially since people have a tendency to downfame posts much more often than upfame them, which greatly affects regular posters with strong opinions. (Don *cough cough*).
I think once we hit the negatives, our votes should have less of an impact, but we should still be able to rate others. JMO.