I know that the lighted keyboards used by the Sonys employs a photo sensor (ie, KB lights up only below a certain threshold of lighting).
I wouldnt worry so much about power draw as a couple simple LEDs would be provide enough light. What would be nice (and what Im not sure about) is whether or not there is provided a capability to override the auto ambient photo sensing (ie, force KB lighting either on or off).
I have another question, for those that use a laptop with backlit keyboard. Do you feel that it's an indispensable feature now, to where you couldn't go back to using a laptop without one?