This confirms what I suspected—the new MacBook Pro battery has a lower capacity than the old one. About 16 percent less to be specific. The old battery was rated at 5600mAh/60Wh, but the new ones are rated at 4700mAh/50Wh. This perfectly explains why you now need to use the integrated Nvidia GeForce 9400M on the new Pro to get the same five-hour (rated, not real world) battery life as you did with the discrete 8600M GT on the previous-gen Pro, despite its use of more energy-efficient DDR3 memory (which would negate drops from the faster FSB) and the same processor clock speeds.
As Ryan points out, this possibly means that as your battery degrades, you'll probably have to a buy new one faster and more often, since the pool of energy is smaller to start with. It also gives fresh urgency to our hope for new TruePower batteries from FastMac, which cram more power into the same space and are some of our mission-critical CES gear.
So you might wanna think twice before going into the 9600M GT-powered turbo mode, though when you boot into Windows, you don't exactly have a choice, since that's the card it uses. [Ryan Block - Thanks Ryan!]