Google is now displaying social profile links in the "knowledge panel" section on the right-hand side of search results for some people. This appears to be mainly the case for celebrities at this point.
Here, you can see it displaying Twitter, Facebook, Google+, and MySpace profiles for Kim Kardashian:
Here, it shows Bill Cosby's Twitter, Facebook, MySpace, and Instagram profiles:
There doesn't seem to be a lot of consistency to Google's approach. There are quite a few celebrity searches that aren't returning these profile links. Granted, Google could still be rolling the feature out.
The profiles displayed vary from search to search. In addition to those above, YouTube also appears in some cases.
Images via Google