Google Social Search is a new, experimental feature just released on October 27. Theoretically, it’s supposed to add functionality to your search page by highlighting web pages associated with your contacts within your results page. All you have to do is sign up within your Gmail account.
Google’s example in recent social search tutorials was restaurant-hunting. If you’re looking for a good restaurant, the best thing is a personal recommendation, but you may not have one. Search for a restaurant name, and maybe someone in your contact list has reviewed it online, or mentioned it in their blog. In this case it should show up in this special portion of your search results page.