Ben Patterson - What sets Facebook Places apart from other Foursquare-like "check-in" apps, however, is that you can check your fellow Facebook users into a place at the same time that you check in yourself, simply by tagging them. So, for instance, if you're strolling into a movie with, say, your friends Pete and Amber, you can check yourself in and check in Pete and Amber as well; all three of you will appear in the "People Here Now" list for that particular theater, and your check-ins will pop up as status updates. (You'll be notified the first time a Facebook friend tries to tag you through Places.)

Source