Google did try this. I don't think it ever left the lab, but I used it for a while. I think they may have canned it; I just realized I haven't seen it in a while. It was called searchwiki. I think it was originally just supposed to apply to your own results, but I'm sure they analyzed the tendencies to see if it would've helful to use overall.

Honestly, such a system would be ridiculously easy to game with a botnet, so there needs to be significant work in the area beforehand.