Mind you, 400 songs at a 256kbps rate gets you close to 3-4GB of data (256 is about the lowest that is very difficult to tell from CD).

How big do these flash drives get?

Could you partition them so they show up as several separate drives at the same time?

Still, let's face it, although many of us have TOTAL repertoires far in excess, how many of us use significantly more than 400 songs IN TRACKS FORM on a regular basis?