I just checked the API and was disappointed there was no way to access the social music graph (a user's friends listen history). If that's never going to be available to third parties, I'd love it if Spotify increased focus on social trends and graph-based music discovery. The "Top tracks among friends" section of "What's New" is great, but I'd love to see trends over time. Even better would be a learning system. This is a sweet spot that rests exactly between last.fm and spotify. My request: Acquire last.fm or build out social recommendation or open up the social music graph to application developers so third parties can write neat social recommendation systems. Last.fm doesn't currently meet this need because Spotify seems to have better and broader adoption, but they probably have the relevant IP and experience.
Regardless of whether you do it in-house or leave social recommendation as an API thing, here's another idea to engage the developer community to build recommendation and discovery systems based on this social data: Have a Netflix-style competition with a small prize. Spotify could get some positive press out of this as well.
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