Facebook has rolled out a new feature called Friendshake that lets you find nearby people via your phone's GPS and add them as Friends.
Head to m.fb.com/friendshake or m.fb.com/ffn (Find Friends Nearby) and you'll see a page like this:
Everyone else who is also on that page within a certain radius of you will appear on a list, and you can then simply add them as friends. It also works in Facebook's iOS app by going to Menu > Apps > Find friends > Other Tools > Find Friends Nearby
Obviously, the idea is to make it easier to meet new friends with similar interests if you're say, attending a concert, or if you meet someone and they want to add you quickly without you having to spell out your entire name.
Of course, do use it with caution, and be aware that when you're on Friendshake, anyone nearby will be able to easily access some basic information about you (such as your name and any other personal information you have set to Public).