The Galaxy Tab also has a 7" display, and it manages 6-8 hours with a significantly lower capacity battery. Android also isn't known for battery life, while BlackBerry is. The PlayBook does of course however have a more powerful CPU. I'd put 8 hours as a minimum, with 12-14 a real possibility.
i would not be happy with a 6-8 hour life span.. but what can i say i dont have the money anyways... but with something that can do soo much i would expect it to be in that 12- 14 range... that would be reaaall nice