Let me tell you where this idea came from.  I have a pretty big music collection... ~10,000 songs, which is not a terribly huge amount, but I keep everything impeccably organized (thanks amarok for making this a breeze).  but occasionally i like to listen to music while i drag files into the playlist for editing.  with big playlists this can be a pain in the ****... enter the collapsing playlist.  what if you could be playing one playlist, then 'collapse it', like the view of the artist/songs?  amarok would know to be jailed in the playlist, so it wouldn't jump out, but it would free up the entire playlist for editing/new playlist/whatever.  upon collapsing, it could just display the name of, say, the current song... no need to name the playlist (unless you want to).  seems like it wouldn't clutter things up too much in terms of the interface.  i don't know how difficult it would be to code - i'm not a programmer.  anyways... thought/comments/whatever?