Another example to look at:

http://www.appsafari.com/games/10766/kingpin-game/

Kingpin, ... is a new addition to the foursquare client family. ... Users can accumulate points, collect badges to store in vaults, and become mayor (boss in Kingpin) of places they regularly frequent. .... Kingpin has all the nifty features of foursquare, but it raises the stakes by allowing users to attack local bosses.