It's a paid streaming service; there's no sharing the actual music with anyone else. It all comes from their servers. That's why there are still large gaps in availability; if they don't have a deal with the distributer, it's not there.

You might be sharing playlists with people on your Facebook friends' list, but it's limited to the music they have available. No difference from the newer US-based services like Rdio or Mog.