Topic: Playlist of Playlists
A feature I would love to see in Cog (and one that I've never seen but always wanted in players for OS X, Windows, Linux) is the ability to create a "playlist of playlists."
A specific example being that one could queue up a entire playlist of full albums and be able to play these albums in random order (while not randomizing the tracks in each album or individual playlist).
One possible solution for this is to have each album folder contain it's own PLS/M3U file, with the ability to "queue up" as many of these user made playlists as one wants, and then play the playlists in sequential or random order.
On a personal note, I am glad there is something like Cog available for OS X. It seems the mac community relies far too much on iTunes and I'm far too 'old school' to like anything other than a media player with file/directory based navigation.