Google rolled out a new experimental Google Labs feature called ‘Google Social Search’ that helps you find more relevant public content from your broader social circle. With Social Search, Google finds relevant public content from your friends and contacts and highlights it for you at bottom of your search results page under the heading "Results from people in your social circle for [you search query]." You can also filter your search results to see only content from your social circle by clicking "Show options" on the results page and clicking "Social", announced Google blog. “Social Search surfaces content in your search results that is written by your friends or people you follow. That way, you get the best resources from the web overall, plus the best results (blogs, reviews, travelogues) that are relevant to you, since they were written by people you know. Marissa at Web 2.0 Summit 09 video,” Marissa Mayer.
Learn more about how Social Search works here, or watch this video: