Apple advertises 8-9hrs battery for the 15" MBPs. My hypothosis is that even under ideal conditions, actual battery life is much shorter.
With a 2010 15" 2.66Ghz i7 MBP, under normal development usage (a few ruby processes, a browser, code editor, MySQL) I get about 3 hours.
Under a controlled "light web browsing" environment, I get 5 hours:
* Dim screen brightness to 50%
* Turn bluetooth off, Wifi on
* Set display to never go to sleep & turn screensaver off
* Use http://http://codykrieger.com/gfxCardStatus/ to set
graphics card to intel only
* Use itunes to play local music at a low volume through headphones only
* Use this script: to simulate light web browsing: http://gist.github.com/441222 . It writes a log so you know when the computer goes to sleep.
* Walk away from the the computer and wait for it to exhaust it's battery and go to sleep.
HNers -- I'd love to get your own datapoints.
I suspect that disk activity has a big impact upon power consumption. But when doing heavy development (and using Fusion) I power from mains.