Just a quick thought: if the Google Glass aims to be a computer you wear on your face that stays out of the way all the time, then the command to take a photo shouldn't be "OK Glass, take a picture". That's cumbersome. It takes longer than pushing a shutter button.
In my opinion, the command to take a photo should just be "wow". It's what you're likely to say when you see something amazing, so Glass should take a photo at that prompt. Just my 2 cents.
Mokalus of Borg
PS - If I had a Glass headset, and you could remap the voice commands, that's the first thing I'd do.
PPS - Besides taking a self-portrait in a mirror, of course.