I think there's a serious bifurcation between "tech-savvy, smartphone-using, social (and generally single) twenty- and thirty-somethings with disposable income and time, living in urban centers" and ... everyone else. If you aren't in that first group (I'm not), location-aware apps and social services aren't going to have a lot of utility. But if you live in Brooklyn, work in Manhattan, go out to bars or restaurants with friends two or three times per week, a service like Foursquare could be really useful: "I'm heading to the subway station ... which stop has a higher concentration of my friends at bars? Do I get off in the Village or Chelsea? Oh? Everyone's at Shake Shack? Off I go!" (and so on)