Google search is still the go-to place for general stuff but it falls short if you wanna tap the collective knowledge of your friends. That’s because Google often knows little about who your friends are and has a hard time estimating the relevancy of their shared content. In 2008, Google has partially addressed this issue with Social Search, an experiment that added to the bottom of your search results real-time public tweets and blog posts by the folks in your social circle. Today, Google Social Search has graduated and is now an integral part of your search experience. "Sometimes when you’re searching, having information from people you know can be really useful," the company explains.
Available in English only and rolling out over the next couple of weeks, Social Search mixes content from your friends with regular search results, provided you’re signed-in with your Google Account when searching. This may include items your friends shared via Blogger, Twitter, Flickr and other publicly available sites. A handy annotation below such a result denotes it came from someone you’re connected to. The annotations include the names and profile photos of the people who shared or published this information, as seen in the below screenshot.
And unlike before, socialized results now include content the people in your social circle shared, not just what they created, like before. For example, in the past Google would only show you tweets about blog posts your friends’ and co-workers’ created, but now you’ll be seeing their tweets promoting someone else’s blog posts as well. Apart from Facebook Page likes, comments and status updates, your socialized Google results exclude likes on third-party sites as well as likes and content posted on personal Facebook walls, unless their owners share this data with "everyone." This is most likely the consequence of Google’s growing antagonism with Facebook. Note that Bing is able to include personal Facebook walls in its search results.
Google Social Search works best if you have a Google profile where you can add links to your other public online social services. Google uses these connections to figure out your social circle. This may include anything from the people you’re following on Twitter or FriendFeed, websites from your Google Reader reading list and Gmail chat buddies to Flickr and Picasa accounts, contacts in your friends and family and coworkers groups.
Also, you can now link your other accounts on your Google profile publicly or privately (previously, everything used to be public). The change lets you take advantage of social searching without divulging your other identities on the web. Google also employs some backend wizardry and will invite you to connect the accounts it thinks might belong to you right on the search results page.
Source: The official Google blog