I was looking for some power consumption data, when I came across this article "Linux vs. Windows Power Usage".

In summary they compare 4 operating systems, and how much power the computer draws to run them.  For example, "While idling, Ubuntu 7.10 was consuming the most power with 41 Watts…. Both Windows XP and Vista were consuming 39 Watts while idling.".  Fedora consumed the least amount of power:

Anyway, I though it was interesting, and worth sharing.  Check the original article for the complete story.