A couple of people in my old team have been around talking about how Spotify does music recommendations and put together some quite good presentations.
First one is Neville Li's presentation about Scala Data Pipelines @ Spotify:
Febrary 6 was my last day at Spotify. In total I spent more than six years at Spotify and it was an amazing experience.
I joined Spotify in Stockholm in 2008, mainly because a bunch of friends from programming competitions had joined already.