One of the things I love about Spotify's mobile app is how easy it is to create and manage song playlists. Users get several contextual options while listening to a song including 'Add to...' (below) which begins a quick playlist management flow.
It just interrupts the user experience and doesn't match the model users have when it comes to playlist management. It's much more fun (and intuitive) to add a song to a playlist quickly, in the context, without leaving the screen - 'Hey, this MBV song would be perfect for that Thanksgiving party we're having!' Otherwise, without the contextual option, the song ends, the moment is gone and the party suffers.
I always thought this could be fixed by giving the users a fourth contextual option (see mockup) to add the song to a playlist, just like other contextual options (repeat, the seldom used Genius and shuffle) you find when you tap the middle of the screen.
That's right - Apple has always had other options for songs but decided to leave the Playlist option out of the equation. From here, users could quickly add a song to a playlist or create a new one, without the unnecessary navigation. I hope Apple adds this functionality soon - although the beta version of iOS7 doesn't address this. Until then, it can be done - just not very easily.