Hadley, I've evaluated Macs for DJ'ing and think a PC card slot for audio i/o, backlit keyboard and FW400 or FW800 are all important. (Optionally, USB could be used for audio i/o - for example Rane MP4.) Having all this in a rugged 12" Mac Pro would be awesome.
Ode to the 12" Powerbook: 14 Wishes for A New Hyper-Portable Macbook