We are using FourSquare for a lot of different things – keeping track of where we have been, finding nearby services, looking at accommodation and restaurant reviews, and reading tips from other 4sq users.
Probably the neatest thing is being able to grab the KML feed from foursquare and pop it into Google Earth. It puts a pin on each location we checked in resulting in a cool map showing all the places we have been.
Australia and New Zealand