A feature I'd love to see on the iPod (and in iTunes) is song aliases or shortcuts.

Let's say I am a Paul McCartney fan (which I am) and have ripped my copies of Band On The Run, Wingspan, Greatest Hits etc (which I have). All of these albums have the same version of the same song 'Band On The Run'. Rather than storing 3 copies, I'd love to have one and a pointer ('alias' or 'shortcut', depending on your OS persuasion) for the other albums.

That way I could play any full album in the way it was intended, but only have one copy.

Now I know there is the singles versus albums debate...