Which brings up another point: I think that if anything is going to threaten Google in the coming years, it'll be the quality of their social graph. Gmail gives them a lot of data, but if my inbox is any indication a lot of it is somewhat ambiguous. Aside from that their social apps haven't done too well (in most places).

Facebook, on the other hand, has developed a system where nearly every user activity creates a new easily processed and meaningful connection between users or out to the web itself. And those connections are probably closer to representations of some kind of trust than "I email that person a lot".

Anyway, I'm not saying the sky is falling for Google, just that search appears to be changing for the first time in awhile.

I don't know about you, but my social graph is pretty diverse. I wouldn't trust all those very different people to make an important decision like "what sites should be visible to me in search engines."

You're right. Others should not be able to hide sites from my search results, but their decision on blacklisting sites can affect the ranking of sites in my search results.

Nobody said you had to trust everyone in your social graph. I definitely wouldn't, but that doesn't mean there aren't a few select people that I would trust.