Social Search, without a Social Network

Google's new +1 button lets friends tune each other's search results, but so far the company has few connections to draw on.
One of the problem is identifying the friends. While Facebook has a clear definition of an individual social network, this is a hard problem for Google. However, Google has the resources to identify "friends" in many different ways.

in reference to: Social Search, without a Social Network - Technology Review (view on Google Sidewiki)