Foursquare for Homework?

I just attended a talk by the co-founder/CEO of Foursquare - Dennis Crowley - who happens to look like Justin Bieber's older brother and is probably just as wealthy. For those not familiar, Foursquare is a location based social network that allows users to "check in" at various venues - bars, restaurants, the gym - and keep track of their friends' whereabouts. Users who check-in often can earn free drinks and other prizes and the person who checks in most frequently at any particular venue earns the title of Mayor.