Battery life is definitely greater. My battery performance on average equals or surpasses what I got on vista with powersaver, and I always use 7 on balanced. Lol, I always run 7 on balanced while I always used vista at maximum, and 7 is still faster.
This is from an old engadget post:
"Now that Windows 7 has launched into pre-Beta, Microsoft has joined the world in Vista-bashing as they look to differentiate their newest OS from the incumbent. Speaking to its hardware partners at WinHEC, Microsoft is promising faster shutdown and startup times and less power consumption than its beleaguered predecessor despite the two sharing the same code base. In addition to an overall reduction in the number of services launched at startup, faster booting is achieved by loading device drivers
in parallel instead of sequentially. Windows 7 also manages wireless radios better allowing them to drop below 100% power draw while managing the connection. And by tweaking the OS kernel, the CPU can sometimes run at a lower frequency and stay idle longer. This results are a minimum of 11% better battery life for Windows 7 compared to Vista -- and we're still only talking about pre-Beta Windows 7 software, mind you. Nice. Windows 7 also promises better memory management. So instead of managing all the background windows, Windows 7 offloads this to the GPU, for example -- system memory is then free for your applications and data. Check the trio of videos demonstrating these improvements after the break."
Link: Video: Windows 7 promises faster boots and up to 15% better battery life - Engadget
Amazingly, that 11% sounds perfectly accurate, if not actually an understatement.
I had also read or heard somewhere that simply by tweaking something with the clock(perhaps it was clock speed, but I'm prettysure it was the plain old clock), Windows 7 gained increased battery life.