MacBook Pro and Built-in Battery

I noticed that the new MBP comes with a "breakthrough" built-in battery feature. I don't currently see this as a positive thing, however. Last summer the battery in my iBook got so bad that when it was fully "charged" and plugged in, the computer worked fine. With the battery in, as soon as I unplugged the AC adapter the computer shut down. I know this is somewhat normal for any electronics battery, that is, to get worn down and not work well after a while. My concern is that this will happen to the battery of a MBP, except with it being built-in I won't be able to just buy a new battery for $40 like I did with my current iBook. Does anyone know if this is not supposed to be a problem or if Mac has a way around it or what? MBP is my top choice for buying a new computer sometime this summer, but that could be a serious drawback. I'd hate to think that the portability of a laptop would become completely shot after 3 years (that's when my iBook battery was gone).

Nevermind, I guess the WWDC speech addressed this issue. Apparently, the built-in battery has 3x the usable lifespan of normal ones. And hey, if I got 3 years out of my old battery, then I should get 9 out of this one...not bad.