Microsoft and Bing are partnering to "make Bing search more social." The main idea is to improve Bing results' relevance by using Facebook Instant Personalization. And to improve Facebook's Web-search results that are powered by Bing. From Facebook explanation of today's announcement: "When you search for something on Bing or in web results on Facebook (powered by Bing), you'll be able to see your friends' faces next to web pages they've liked." Don't worry: You can opt out.
The actual deliverables are two new social search features Microsoft and Facebook developed in tandem. They'll begin rolling out to users on Oct'13 and will continue to populate in "the coming months."
The features are "Liked Results" (recommendations from their Facebook friends built on Facebook's public "Like" feature), which uses Facebook "like" information to help you discover new information and get more personalized results in Bing.
And "Facebook Profile Search" which'll provide user-search results based on their relevancy to searcher's Facebook network and friends. Also enabled you to take action and add the friend, or even send them a message to make the task of finding the right person that much easier.