Google launched a social search option in 2009 and now has introduced some improvements aimed at better integrating search results and recommendations from your social circle into Google's search results.
Instead of appearing at the bottom of the page, social search results will be mixed into the regular search results, based on relevance. Additionally, notes below search results will show Facebook and Twitter contacts who have shared the link, along with their photo so you can see which stories and pages your friends are recommending.
Social search has always used contacts pulled from Google to determine your network, but now you're able to privately connect accounts you don't necessarily want made public, like your Twitter user name. If you choose to privately connect your accounts, they won't show up on your Google profile.