The thing about Colemak is that if you ever have to use somebody else's computer for a moment, you can be absolutely certain they don't have it installed. Dvorak, I think, strikes the most acceptable balance between efficiency and widespread availability. Sure, as a hacker, you should set up your own unique keyboard layout/.emacs file/guitar-pedal-to-USB modifier keys/saccadic eye motion detector/whatever to absolutely maximize your efficiency for how you spend most of your working hours, but if the day ever comes when I'm the only person who can override the Doomsday Machine, I could do without the hassle.