I have zero interest in meeting random people via Foursquare -- however, the "explore" functionality is awesome. The competitor isn't Yelp (outside the Bay Area), but TripAdvisor, which is really the only service which great coverage of a lot of places.
I have been in the SF bay area, NYC, Europe and looked up TripAdvisor all the time. I tried to see if Foursquare provided any more useful information. Unfortunately, none.
