Microsoft expanded its partnership with Facebook on Monday, melding Bing search results with data from the Facebook network of the person doing the searching. The new "social search" features — you'll see what stories and products your Facebook friends "like" in your search results, for example — are an assault on the dominant search engine, Google, which just launched its own social search feature, called +1. Can Facebook and Microsoft do together what neither has been able to do on its own, and humble Google on its own turf?

Google can't win this round: Google "recognizes that social search is increasingly important," says Juan Carlos Perez at Computerworld. But its nascent +1 feature won't pose a real threat to Facebook's mighty "like" button. And thanks to their bitter rivalry, Google will probably never have access to Facebook's valuable trove of social data. Now Bing does, and "the deeper the access to its data, the better for search engine providers."
"Microsoft deepens Bing's use of Facebook data"

Microsoft could score major ad money: Bing would undoubtedly like to overtake Google in search, but this Facebook deal isn't about raw search numbers, says analyst Charlene Li, as quoted by the San Jose Mercury News. If people end up trusting Bing's results more, "advertisers will follow." Marketers don't care "what the population of Kazakhstan is. Let Google take that." Bing wants people asking, "Where am I going to take my kids on vacation?" That's ad gold. And knowing what Facebook friends recommend is a major selling point.
"Microsoft's Bing gets help from Facebook to compete with Google"

Though the new Facebook integration is a little creepy: Microsoft is banking on the idea that you'll want your Facebook friends' virtual input when you search the web, says Greg Lamm at TechFlash. And that may be true. But they're also "banking that most people won't give a second thought to allowing the search engine to access their friends list," plus photos, user ID, and, in Bing's words, "any other information I’ve shared with everyone." That was too much sharing for me.
"With Facebook's likes, Bing hopes to become more relevant"