(the future of green computing- ASUS' bamboo laptop)

It's often the easiest things that can add up to have a big impact. The simple act of turning off your computer at night could save you up to $90 a year not to mention the kilowatts saved. Although many of you may know this, it's important to remember that a screen saver does not save energy, so be sure to set your computer to standby or hibernate when you aren't using it to dramatically decrease the energy consumed.

(more specifics here and here )