Neither can Apple.
It's a very widespread issue right now, but it absolutely does not happen on all of them. See below.
I certainly hope so, but I have confirmed first-hand that two identical units can have exactly the same software and firmware while one unit has the flicker issue and the other one does not. In fact, I currently have three unibody Pros (long story how that happened): two 2.4 models and one 2.53 model. One of the 2.4 models (my wife's) has absolutely no flicker under any circumstances whatsoever, while the other 2.4 flickers at low brightness on both GPU configurations---but only when spinning the hard drive. These machines have exactly the same software and firmware. In fact, I can (and have) swapped the hard drives between the two and nothing about their flickering behavior changes. (This wouldn't change the firmware picture, of course.) The 2.53 model flickers much more offensively than the naughty 2.4---but only on the 9400M at low brightness and independently of hard drive load. It also has all the software and firmware up-to-date. Both flickering machines exhibit this behavior independently of power source.
I can also confirm that the 2.53 flickered before any of the recent firmware and software updates Apple released, and that it continues to flicker when installing a clean version of 10.5 all the way back to 10.5.4.
These findings are the result of my testing over the last week or so. They lead me to believe that software probably won't fix the issue. Firmware might, but it would be easier to suspect firmware was to blame if they all did it when running identical firmware versions, and they don't. I think problems with power flow in the logic board are to blame. My 2.53 unit is now waiting for a replacement logic board to arrive, to see if that will fix it. The bad 2.4 is going back today.
