Bing has expanded the functionality of its social integration to include any and all URL's that are displayed in the results pages and Facebok integration. This change comes on the heels of Google's announcement that they will be including socially-driven content in their results. Bing has already been integrating Twitter into its search engine results and this step into Facebook can keep the search engine up with Google.
The point behind a social layer on the search results is the belief that people will value the things that people they know like and post to their social networks. This will bring a more personal feeling to the results pages. If you are searching for information and happen to see what your friend likes, you are more likely to make an educated decision.
This follows the direction of search engines to a simple, one site search for everything that the end user needs. Every search engine is looking for the newest and best for its users, and with integration of everything from social media to maps and news, they are making it easier for its users to find everything they need all on one site.