I have also experienced the strange freeze while randomly working in X.
At first, I believed the freeze was caused by my laptop heating up to ~65C. So I bought a under-cooler bringing the temp down to 52C. But I continued to see freezes. I screwed around with drivers for quite some time, again no help.
I found this topic and followed a few suggestions I found. The first one, i switched to the "nv" driver in xorg.conf. But still, I experience random freezes where the mouse & keyboard lock up. The only thing I can do is to hard reboot the machine. Surprisingly, I can still change the brightness of the screen and some other features built-into the laptop. I have isolated the problem to a few causes.
#1) When I am running a cpu-intensive program, the laptop begins making a good amount of noise (due to fans starting), and the laptop carries out the process. But as soon as the cpu intensive process ends and I close the application, the laptop freezes. An example is playing a flash animation on a website using firefox, and then closing firefox. This repeatedly causes the laptop to hang.
#2) Firefox, for some bizarre reason, firefox spikes the cpu and causes the laptop to hang. I have no idea what causes this spike, they usually appear during causal browsing.
My best hope right now is for 2.6.11 to fix this problem, but I have tried the vanilla sources from kernel.org and have gotten the same problem.
Also, I have played with kernel settings, enable/disable ACPI and APM, none seem to make any difference. My main concern is that even with "nv" in my xorg.conf, I still get freezes, which leads me to believe this is not an nVidia problem, but possibly a kernel/xorg problem. I have viewed all the logs I could find, but none state anything about the freeze, the machine simply stops responding to user input.
My laptop:
Dell 5160 Inspiron
p4 3.0ghz HT (ht is enabled in kernel config)
It seems the longest I have ever gotten the laptop to run before a freeze was with "nv" and using wired ethernet (wireless disabled). This allowed me to run for a full 3.5 hrs before a freeze. Please assist in any way possible! Thanks!

Hello World.