I think there's a lot of interesting/useful stuff you can build on top of location-based service like Foursquare once enough people actively use it. I've alway

I think there's a lot of interesting/useful stuff you can build on top of location-based service like Foursquare once enough people actively use it. I've always thought that Foursquare's initial check-in game is more about this bootstrapping phase: how to make Foursquare even remotely interesting, when none of your friends are yet using it. I've seen tons of startups that have cool ideas, but that require dense graph of active users to work. They rarely have good ideas how to get to that phase. I think Foursquare has been a super-clever using game mechanics in the initial phase.