Foursquare was the most talked about new app around when it launched at SXSW two years ago, and the location-based social network has done a commendable job so far converting the early buzz into long-term sustainability. This year the service added its 10 millionth user, and just last week it clocked its 1 billionth check-in. Watch a neat video Foursquare posted illustrating check-ins as they happen all over the world above.