I think a personal black-list would be ideal initially as those most motivated would be most helped, i.e. the majority of people who might not care about the st

I think a personal black-list would be ideal initially as those most motivated would be most helped, i.e. the majority of people who might not care about the status quo are then not impacted at all. As mentioned above, then introducing the shared-ranking via the social graph would be the next logical step. It could be something opt-in'd to ease adoption. Then, ideally (and this is my personal 'white whale' problem) it would be great to imagine something where the user could whitelist through no action of their own rather than have to do any work to block, i.e. use the result set 'hit' of what's clicked in the results to act as a personal ranking upvote. There's some interesting engineering issues of per-user indexing though, but hey, you wanted to work at Google right?