I had a fun time at Music Hack Day London 2010, despite only being there physically for the Saturday. The team, made up of Yves, Chris and myself, with camerawork provided by Patrick, created an Android app to discover musical treasure. It won the 7digital prize.
Technical run down: the Android app allows you to drop tracks from your personal playlist at any point in space. This POSTs your coordinates with the track and artist name to a Rails app. The Rails app then looks up the track’s clip on 7digital using Echonest’s API. If it can find a clip, a clue appears in an atom feed (and on the Piracy homepage), which also gets tweeted courtesy of Feedburner.
As well as appearing as a clue, the track will start appearing on Android phones running the Piracy app when the track is within a 200m radius. If you happen to be in one of the London postcodes in the clues, you can try to find the tracks that have been previously dropped (though it might take a bit of walking!).
Both the Android app and the Rails server are open source on Github. As the POSTing is pretty slow, we don’t imagine that, without implementing a message queue component, the app will withstand too much traffic. Maybe we’ll get time to fix that!
Also, if you look through the Rails source, you’ll see there’s some piratey-themed cucumber stories, and a far easier way to find the tracks. We should fix that too 
It was great hacking with you folks! Hopefully we can improve the hack in our spare time.