Foursquare is pretty neat. You can post you location via phone or browser and get nifty badges for different things or become a mayor of a place if you check in to that location the most. Its also exceedingly easy to cheat at.
I only casually mentioned the idea of cheating to @Jack_Mannino and within a few minutes of emailing him the link to the API he was already traveling the globe at record speed.
Foursquare even has a nifty and pretty easy to understand API here:
http://groups.google.com/group/foursquare-api/web/api-documentation
The simplest thing you can do is checkin and post your location by vid or venue.

