While searching for a friend on Facebook, I suddenly noticed that I was being served search results on the side, that were "powered by Bing"
Apparently this started a couple of weeks ago.
Pic below for searching for Google, with the search results block in red.
Facebook usage does lead to searches; some study a while ago showed that Facebook users tended to increase their Google searches, and I can believe that given my own behavior.
Bing is pushing hard to acquire traffic. I can hardly do a general-ish query on Google without being served an ad for Bing.
Not a bad way for Microsoft to make use of its investment. :)