Google has quickly tried to counter Bing and Facebook's social search announcement by integrating social shares into their main search results.
As you can see in this screenshot, there is a "Shared by 20+" notation next to the name of the website and number of related articles.
This "shared by" link only appears on the main Google search results page. If you were to click on the "News for ses chicago" link, the shares don't carry over.
Clicking on the "shared by" link brings you to Google Updates, which shows real-time sharing activity.
Also, on some of Google's Hot Topics, (e.g., Christine O'Donnell), you'll also see a message that says "x recent updates from Twitter, MySpace, Facebook, and more for Christine O'Donnell."
Interesting update, especially considering all the talk of the Bing/Facebook search revolution. Not sure yet if this is a test or if this will is a permanent change.