Nvidia's teasing a new notebook tech called Optimus that "get[s] the performance of discrete graphics from a notebook while still delivering great battery life." Which could solve the mystery of the next MacBook guts.
A brief recap: Intel's new Arrandale Core i5 processors for notebooks have integrated graphics built right into the chip, but they suck, and Nvidia's chipsets with superior integrated graphics, like the current MacBooks have, are incompatible with all of Intel's new chips. So if refreshed MacBooks were to use Intel's integrated graphics, they'd have worse graphics than the current models.
The top-end MacBook Pros have switchable graphics and have had them since the unibody debuted—integrated GeForce 9400M to save battery life, discrete GeForce 9600 GT for more power. Nvidia's Optimus, if it's good, seems to open a door for Apple to use straight-up discrete graphics, like older MacBook Pros (and even PowerBooks), without seriously harming the massive battery life that's a big part of the current MacBook Pros—maintaining graphics performance and battery life without some kind of custom hardware arrangement.
And it wouldn't be the first time Nvidia's debuted new tech with Apple, since that was exactly the case with the GeForce 9400M chipset/graphics that's in almost all of Apple's current machines, which you might also know as Ion, Nvidia's better-graphics-for-netbooks chip.
My guess is that it's simply scalable performance, trading off battery and performance as efficiently as possible. Guess we'll see, and know more, in about a month, according to Nvidia. [Nvidia]