I get a good 6-6.5 hours on avg. under my normal use (Safari, iPhoto and iTunes), on ~4 bars screen brightness, 1-3 bars backlight keyboard, bluetooth off, auto grfx switching ON, auto dim when on battery energy savings option ON, no peripherals plugged in, no external monitor. A full battery can also play two full ~hour and a half movies back to back (from HDD, not DVD player, haven't tried from DVD player since I just rip to HDD). All of my friends' PC laptops get about 1/2 of what I get, battery power wise, when doing the same things I do.
I stayed over a friend's house once who just got a new Toshiba laptop with Windows 7, and when I plugged in my MBP to charge, he asked "already?", to which I replied "I haven't charged the battery since the night before yesterday", to which he then said "oh", as he had charged his battery 2-3 times during the same time. Our batteries rock, and we don't even need to pay extra $$ for an "extended life battery" - it comes standard
If I turn off airport, bluetooth, backlight keyboard, all apps/programs and 1-2 screen brightness bars, my battery icon will show 8-9+ hours life. I do calibrate my battery once/month, as recommended.