I have a new 1.33 GHz 15" model. I am getting about 2.5 hours of battery life with moderate use (Word, a little Illustrator, Safari, TeXShop, lots of copy/paste). I have it set at the "longest battery life" energy saver setting, and the brightness of the display is set a couple of notches below maximum brightness. No cd/dvd use, but I am using Airport.
I was hoping for more, frankly. My Pismo's battery used to last for what seemed like forever (4 hours, maybe?). Last fall, though, it just stopped holding much of a charge (now it is about a half hour). And its dvd drive stopped working. And the HD is full. So I have finally replaced it with this new unit. The screen is beautiful and it is fast. But I sure do like my Pismo. My ideal machine would be a G5 Pismo with a 15" widescreen display. Sigh.