Google Social Search is not a new feature, but it wasn't that important until now. Google used to display at the bottom of the search results page a few links to pages created or recommended by your friends and social connections. The feature automatically obtained data from Google Reader, Google Buzz, Gmail Contacts, Twitter and other sites linked from your Google profile.
Google's blog announced that Social Search will be used to enhance Google results and will become a ranking signal. Social Search borrowed Hotpot's interface that annotates results with messages like "Dan rated this place 5 stars", so you can see why a page ranks so high.
"Social search results will now be mixed throughout your results based on their relevance (in the past they only appeared at the bottom). This means you'll start seeing more from people like co-workers and friends, with annotations below the results they've shared or created. So if you're thinking about climbing Mt. Kilimanjaro and your colleague Matt has written a blog post about his own experience, then we'll bump up that post with a note and a picture," explains Google.
Sometimes a web page is more valuable if it has been recommended by a friend because you probably trust that person. Google uses data from your Google account or publicly available data to generate a list of social connections, but you can't highlight the people you trust or customize the list. What you can do is to add links to your Google profile and to import data that's not publicly available. The Google Accounts page will include an option that lets connect your accounts from services like LinkedIn and import your contacts.