Foursquare is a very interesting internet app across website and mobile. There are many highlight features on it. The GPS & Tweet integration is impressive for users. The other side, compared with twitter page, user and place page are very special in foursquare. The relations in foursquare are added "including", "included" besides "following", "followed". Maybe it provide new "role" to stars, places, companys. (the original role is "@" in twitter)