Clones of it fell into a tar pit: founders were told Foursquare would own the space, and clones that did not pivot out did not work. Foursquare itself is now a B2B business.
Lost its social lead by betting on a person at a place when users wanted to share a moment. Google Maps, with over a billion users, copied its utility features within a couple of years, and Foursquare is now a B2B data and API company.