My Lenovo 3000N200 laptop has been playing me up. When I've been fully loading the processor or driving video hard it's been shutting down because of overheating. I suspect periodic SMIs are detecting an overheated CPU and the BIOS just stops the machine to avoid it turning into toast.
Suspecting that the latest 2.6.35 Maverick kernel was the cause I booted with a 2.6.32 Lucid kernel and that didn't help, so it didn't look like an obvious kernel regression.
Well, perhaps it's getting old and cranky - it's nearly 3 years old. Perhaps the thermal paste between the CPU and the heatsink is not working like it should. Since it was most probably a hardware issue I downloaded the service manual and got out the trusty screwdriver and opened it up. Lo and behold 5mm of dust had accumulated over the fan grill which wasn't going to help the poor machine offload all that heat out of the laptop case. I removed the fan, gave it a good clean and removed all the dust from the fan outlet grill.
After reassembly the laptop was good as new. Instead of rebooting at 95+ degrees Celsius the Lenovo now runs happily.
The moral of the story is that I should regularly service the fans on my machines. Cooking the CPU is something I would like to avoid in the future.