i don't want to flood my facebook friends with checkins everynow and then. That's why i use foursquare. it is specialized for discovering places and know where your friends are.
foursquare is not a feature, it is an experience. Foursquare is for checkins like instagram is for photos or Google maps for maps. Since facebook has photo sharing,it does not mean instagram is in trouble. when you are really good at what you do, it does not matter. Foursquare really matters for cities. in 5 years from now, almost everyone will have a smartphone and people will(already are) start adding more useful digital information to real world places. These informations are going to be their assest. in longterm,foursquare is going to be huge if they execute in the right way.