Yesterday on Slashdot there was an article about Vista's Aero Glass draining battery on laptops faster (to which I say, that should be on the front page of Slashdot?)
In any case, one commenter brought up the point of wondering whether MacOS X uses less or more power than Vista. Today, using my new Mac Mini (which runs Vista 99.9% of the time) and trusty Kill-A-Watt, I did some very unscientific tests.
Idle w/no apps open
Vista Aero glass: 21w
Vista Basic theme: 17w
MacOS X (Finder): 23w
MacOS X (login screen): 26w
Bottom line, you should not get any better battery life by using MacOS X over Vista. In fact, you can get better battery life with Vista because you can turn off Aero glass, but on MacOS X, you cannot turn off transparency/gpu effects.
Just for kicks, I wanted to find out what the Mac Mini consumes when doing some processing:
Folding @ Home
MacOS X: 59w
I turned on my old, very loud machine (2.8ghz Northwood P4), and ran the same tests (using Windows XP)
Folding @ Home: 165w
BTW, my 20" Dell LCD monitor? 48 watts. Turn off those monitors when you're not around, folks!