At altitude, the hard drives basically seize up, and the LCD displays develop a faint spiderweb pattern that makes the picture difficult to discern. Once they come back down, things start working normally again -- the hard drive starts spinning again and the LCD goes back to normal. Above a certain level though, the traditional laptop technology just doesn't work right.
He mentioned that they used to use original hard drive based iPods for data collection they do at the summits, but the flash based Nanos are much more reliable for their needs (not to mention smaller, lighter, and longer battery life...). Once the laptops start shipping with some kind of reliable solid state storage, they'll migrate to those also.