If Custom mode had just a few more features I could forsee some pretty powerful uses for it.

1.) More than 3 filters
2.) Save/Load ability for filter choices

With these in place I think users could get some pretty impressive results very quickly.

For example, this would open up an easy way to batch genres together. Say you are in the mood to listen to a bunch of "softer" genres like Country, Folk, Jazz, R&B and Vocal, but don't want any of the "harder" ones--that day you don't want any Punk, Metal, Hard Rock, etc.

Okay, make it even more selective. Say that you want the above limitations, but you ALSO don't want to hear any Frank Sinatra, Hank Williams or Joni Mitchell songs.

Certainly the Boolean logic used by the Custom mode could set this up easily (asuming there were more filters made available), and with the addition of a save/load interface for the filters, just about ANY combination could be accomplished.