Spotify Premium flatly doesn't work offline.  If you open the app when offline, sometimes it just says you're offline, and shows nothing.  If you have a playlist playing and your cell network goes flaky, it'll simply fail to play further songs.  It'll hang as it switches tracks.  It'll play 3 tracks and then fail to shuffle more tracks, and just have the playlist end until it can get a connection.

I've tried uninstalling and reinstalling, rebooting the phone, and toggling airplane mode.  It simply doesn't play songs offline.  It downloads all these songs to the device for offline mode, then simply can't play the playlist offline?  How does that make any sense?  I mean it's nice it saves me bandwidth, but what's the point if it won't play the next song until the network comes back?

Sometimes, when it decides it doesn't want to play a song, I have to just skip to the next one.  It refuses to play that song until I kill and restart Spotify.