Soundtrckr is a streaming music client with an added social twist. It uses your GPS location to create an automatic social networked based on people around you who are also used the app, allowing one to see what other people in your town or city are listening to.
The software also comes in an iPhone and Symbian version, so there are already plenty of people using the app.
Soundtrckr is free and can be found in Marketplace here.
See a video review of the iOS version after the break.