Google these days provides "social search" results, meaning that it lumps in along with your regular search results links to your friends' social activity where that activity is relevant to your search. Google is up front about what it knows about who you know on a page called the "Social circle." You can see yours by clicking here.
That first look at the list can shock you. There on the page is everyone you know along with everywhere they go -- or at least the online destinations they've decided to publish, presumably.
The list contains people you talk or chat with using Gmail or Google Talk, plus your social networking connections from a wide variety of Google and non-Google services. For each person in your circle, it then shows the services they use, and also their blogs and other streams.
People who visit their social circle tend to look at the list, make an abbreviated "Huh!" noise, then move along, not sure what it means or what should be done about it.
I'd like to suggest a few ways to get some immediate value out of your Social circle:
1. Follow people on other services. Your Social circle is no doubt a mixed bag, with people who post great content and others who have nothing useful or interesting to say. It's a good idea to look at the links associated with the most interesting people, and see if you want to also follow them on other services. For example, if you're following some entertaining genius on Twitter, you might follow their Buzz feed as well.
2. Find the blogs of interesting people. Some of the most interesting social networking commentators have blogs of their own, which are likely linked on your Social circle.
3. Find new services to try. These include not only social networks, but photo and video sharing sites and others. If you see some services you've never heard of, you can check them out by clicking on the links. This is a surprisingly good way to discover other social networks.
4. See what you're sharing about other people. Your Google Social circle shows you a list of all the connections you're making public on your Google Profile. If there are people you don't want to be publically associated with, for whatever reason, you can remove them.
5. See who else your connections are connecting to. The bottom list on your Social circle includes people who are connected to the people you're connected to. So, for example, if you follow Bill and Bill follows Sue, this list will link to Sue and specify that you are (theoretically) connected to her via Bill. What's great about this is that you can find new people. Hey, if Bill is following her, she must be pretty interesting -- that sort of thing.
At the very least, everyone should spend some quality time with their Social circle, just to find out what Google knows about you and your online connections – and also what anyone can know by simply looking at your public profile.