For anyone who's interested I'm currently building a few social features for Spotify at https://volt.fm.

You can already create a profile and share and compare your stats with your friends. You also get a nice page for your playlists (see https://volt.fm/playlist/x48gzqnr2xoctxu1).

I'm now looking for beta testers for the next big feature that lets you share music (and play what's shared with you) right within the Spotify apps. Let me know if you want to join the list.