I have installed both Win 7 and Win XP on the following machines:

T43
X61
X60s

My observation is that I lose about 20-25% of battery time (on average) when I use Win 7 when compared to Win XP. Does this sound correct?
I thought Win 7 would have better battery time or is it the other way around?

Definitely sounds right for the T43 in my experience, can't say anything about the other units...

I have a T41 and X60, both with multiboot systems, and the same here ... Win7 is far less energy efficient. XP gives 20-25% better battery life. But better than them all though is my X31. Amazing battery life with that OLD laptop. Go figure! (see sig for laptop spec's)