I hate being tagged on Facebook but I might be out of the norm.
I guess this is a useful feature.
You search for something, can't find the best answer on Bing and decide to ask it on Facebook and call out some friends who you think are experts in the area. It will add notifications to your friends notification menu and encourage (annoy) them to answer.
What do you think of this feature?
Here is a video of how it works from Bing:
Forum discussion at WebmasterWorld.