I use sleep/hibernate modes to save energy use in general-

[A typical desktop computer uses about 65 to 250 watts. ]

[Modern computers automatically go to "sleep" when you haven't used them for a while, drawing only 0-6 watts. (Putting the computer to sleep also sleeps the monitor, on most models.) In the past, turning on the sleep setting was the most important way to save on computer energy use, but now that the sleep option is turned on by default out of the box, that's pretty much done for you. Just make sure you don't override it by turning it off. Of course, you can go the other direction, tweaking your sleep and power usage settings, especially by having your computer sleep sooner after a period of non-use. Here's where to set your options:]

[A screensaver that shows any image on the screen doesn't save any energy at all]

http://michaelbluejay.com/electricity/computers.html