This is yet another iPod related post, but only because ripping DVDs for the iPod seems to use more CPU power than anything else, including Illustrator and Photoshop. I am using Handbrake and once the process starts, so does the PowerBook's thermostatically controlled fan. And it stays on throughout the several hour process.
It's kinda worrying to hear this continual noise, so I downloaded Temperature Monitor Lite and now keep an eye on the sensor immediately beneath the processor. Right now it's at 146.3ºF (I am ripping a DVD while I write this). Normally it would be at around 110ºF.
This entire experience is why Apple switched to the much less energy abusive Intel processor family. My PPC-equipped PowerBook generates enough heat to keep my hands warm in the middle of a Canadian blizzard!