The premise is simple: people value their acquaintances’ content more than that of random strangers.  So Google Social Search brings content from your social circle to the forefront, perhaps showing a friend’s or coworker’s take on a restaurant rather than (or in addition to) whatever the local newspaper reviewer had to say.

On the Official Google Blog, Maureen Heymans and Murali Viswanathan explained, "The way we do it is by building a social circle of your friends and contacts using the connections linked from your public Google profile, such as the people you’re following on Twitter or FriendFeed. . . .  If you use Gmail, we’ll also include your chat buddies and contacts in your friends, family, and coworkers groups.  And if you use Google Reader, we’ll include some websites from your subscriptions as part of your social search results.