I've started to use Foursquare... Again. I quit this service months ago, because it was basically a social game, where you tag yourself and get badges (or even become the mayor of the place, bitch!). It became useless and boring after few weeks.
However, I've rediscovered Foursquare and now I use it with pleasure, because it's becoming a social experience to discover new places and get useful advices. It's a sort of city guide... better, a "place-guide", based on your location, your own preferences and the places that your friends have visited. Furthermore, you can use it to find places that satisfy your wish of the moment, for example a place to drink a good beer.
If your're not using it, give it a chance; if you were using it time ago, try to rediscover this social as I did. It's becoming really nice and not only a useless social game.