Social search had been on my mind for two and a half years now. Back then, I expected Google (Nasdaq: GOOG) to buy Twitter and use the microblogger's conversational technology to transform search. Microsoft (Nasdaq: MSFT) couldn't remain idle, I argued, calling on CEO Steve Ballmer to make a bid for Twitter before it was too late.

"When it comes to search, it's important to understand the sources to which we ascribe value. Friends are more valuable to us than strangers, but strangers also have value. Social networks have seen to that by providing a mechanism for indexing groupthink [and] Twitter aggregates these digital conversations better than any other platform on the Web," I wrote at the time.

Microsoft is finally listening. Last week, Mr. Softy expanded its partnership with Facebook to include deeper integration with the Bing search engine. The idea: Let your friends help you make better decisions about what to read, where to travel, what to buy, and so on. Here's a closer look at how the two are cooperating: