Microsoft's Bing has integrated Facebook "Liked Results," which highlights links that your friends have publicly shared or liked.
The move is the result of Microsoft's partnership with Facebook and illustrates how search is trying to be more social. Microsoft surfaces Facebook while Google integrates Twitter in results. The big question for Google is whether it can have social results without Facebook.
In a blog post, Microsoft's Bing team explains how social will integrate with search.
While we are very excited to talk about our next development, we’re all aware that it’s all part of a longer journey. This is the first time in human history that people are leaving social traces that machines can read and learn from, and present enhanced online experiences based on those traces. As people spend more time online and integrate their offline and online worlds, they will want their friends’ social activity and their social data to help them in making better decisions. Integrating with Twitter data 16 months ago was one step, and exploring Facebook’s rich streams is another.
Bing noted that the Facebook Liked Results won't turn up in all searches. Indeed, I tried a few that I know have likes in my network and couldn't turn up any.
The upshot to all of this is that Google and Microsoft are looking to social networks to enhance and supplement their respective algorithms.