The software is Debian Sid. I had this problem, dist-upgraded and it still occurs. I am inside X when the crash happens, I have not tried closing X down for the day to see if it repeats. I am running kernel 2.4.17, and whilst I did have crashes in previous kernels (I jumped from .13) they were not daily.
I had a similar problem twice: 1) after installing nVidia drivers (maybe it's an X/videocard driver prob) 2) It'd just randomly do it, even in (cough cough) that *other* OS (splutter) so I attributed it to hardware. It seemed to fix itself.
I'd go with Mark, maybe focussing on X and/or video drivers, and then going for the kernel. Not much help either, I'm afraid!
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