The result of my work there is TuneMap, a web app developed by Alberto González, Guiller Malón and myself, using the Deezer‘s and Echonest‘s music APIs. We had little sleep but lots of fun. And it was worth it: we received prizes from the Deezer guys!
Lots of cool hacks, including TuneMap, can be found in the Music Hack Day wiki. Drop by and enjoy!