On its sixth birthday, Facebook launched a host of new features as it crossed the 400-million user mark.

The most interesting of them may be its revamped search. When you type in names, it auto-completes for people who are the closest to you by social promixity — e.g. the people that you have the most mutual friends with. Not only that, Facebook CEO Mark Zuckerberg says that it indexes content two degrees out in your social graph.

With the new privacy settings and more public content, search should figure increasingly prominently in the user experience as it will be able to surface more and more content over time.

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