Details are scarce but according to The Inquirer NVIDIA is having heat problems with their upcoming G92 GPUs. The site expects the problem is that the coolers they ordered can't get the chips chilled enough:
This means the chip will have approximately the power density of a modern CPU, assuming they didn't up the wattage by a lot. This is quite controllable; if ATI could do it on the X2900XT, the G92 should not pose much of a problem.
So, where does that leave us? I am guessing, and this is only a guess, that the cooler they ordered isn't exactly cutting it on production silicon in a real case. I can't think of another reason why they would have to jump through so many hoops so late in the process.
In any case, word should be leaking soon enough, and we will then know if we have another 5800 or 8800 on our hands. One thing for sure, you won't be seeing them in laptops, especially Montevina ones.
This news sounds a bit weird as we've also heard reports today that the GeForce 8800 GT will be a pretty good overclocker.