For the past year, Bing has been customizing search results based on the recommendations expressed by the number of times a user's Facebook network had pressed a "like" button on topics related to a search request. Gurry said Bing discovered that most Web surfers didn't want the results influenced by their friends to be co-mingled with answers generated by a computer program.
That culminated in the decision to create Sidebar so a separate area of the results page is devoted to the social-networking suggestions.
Bing's experience underscores the difficulty that all search engines have had figuring out how to blend the influence of social networking into their results, said Altimeter Group analyst Rebecca Lieb.
"Different parts of the social graph are good for different reasons," she said. "When I am looking for advice about a movie, I probably don't want to see a recommendation from one of my 'foodie' friends. What Bing is doing looks like a very elegant approach, but it remains to be seen if people are going to like it."
Lieb doesn't believe it's a coincidence that Bing is announcing its Facebook-friendly makeover as the world's largest social network prepares to complete the biggest initial public offering of stock in Silicon Valley history. The media frenzy surrounding Facebook Inc.'s IPO, expected next week, can only make more people more curious to see how Bing is highlighting results from the social network, Lieb said.
Microsoft has been working closely with Facebook since it bought a 1.6 percent stake in the social network for $240 million in 2007. It has proven to be a tremendous investment. Microsoft's Facebook stake is now worth $900 million to $1.2 billion, depending on the price set in the IPO.
And now Bing can pore through the reams of information being posted by Facebook's more than 900 million users, 18 times more than the social network had when Microsoft bought its stake.
Twitter also has been selling Microsoft expanded access to its tweets since 2009. Google Inc. lost its special privileges to the same stream of data last summer because Twitter didn't renew a licensing agreement.
That partnership unraveled right around the same time Google launched its Plus social network to counter the growing popularity of Facebook and Twitter. In a move that has amplified questions about its objectivity, Google began this year to favor results drawn from Plus while excluding publicly available information from Facebook and Twitter — data Google doesn't need a licensing deal for.
The bias has provided more fodder for an intensifying Federal Trade Commission investigation into allegations that Google has been stifling competition by highlighting its own services and burying or completely ignoring links to its rivals' websites.
Despite Microsoft's massive investments in search, Bing hasn't been able to ding Google so far. Microsoft has nearly doubled the 8 percent share of the U.S. search market that it held when it rolled out Bing, but virtually all of those gains have come at the expense of Yahoo.
Google ended March with a 66 percent share of the U.S. search market, up by a percentage point from June 2009 when Bing entered the fray, according to the research firm comScore Inc. Bing's share currently a distant second at 15 percent.
Unlike its rival, Bing intends to include relevant recommendations from a wide range of social-networking services, including Google Plus.
"We are not trying to build an empire by favoring some services over others," Gurry said.