Bing's "social search engine" positioning does have a unique proposition. Their new Friend Tagging feature could tap the social network you actually use to aide your search results. You can now tag your Facebook friends in any given Bing search with Friend Tagging, and directing your query at them.
You can do it in the Bing social bar, right on the page, which makes it convenient. Or you can send an email as well. Which boils down to the essence of this. You don't have to rely solely on Bing for your answer.
It's a really interesting way of searching, though those who get tagged better be those who wouldn't mind contributing or helping you. The feature could serve as a handy way to make sure your friends know you want their input, but again, only if they really care about it.
Google is also trying social search with Google+ results, but its most likely a Facebook integration that could make social search what you might actually want to use. [Bing Search Blog via The Verge]