To see Google social sitelinks in action, check out the screenshot below:

According to Google, social sitelinks are are based on the same technology as Google Social Search; we use your social circle to identify relevant websites and user pages.

If the social sitelinks don't automatically appear in your search results, Google suggests you create a Google Profile and add links from the networking sites you use (e.g. Facebook, Twitter, MySpace and YouTube). You will then have an online social circle of trusted people whose public online content will surface every time you search.

The quantity and quality of social sitelinks that will appear in your search results will largely dependent on how active you and your contacts are with social media.

So why not search for updates from friends on networking sites directly? Maybe Google is trying to do what Facebook has already done well, keeping your friends close by for all your search activities.