Happens on a brand-new 2.53 Ghz MacBookPro6,2(Intel HD - built-in, Nvidia GEForce GT 330M - x16 PCIe). I occasionally use a 24-inch Dell FP monitor at work, but this happens with or without that monitor being connected at the time of the freeze.
/var/log/kernel.log spews these exceptions by the dozens per second. The machine is unusable, perhaps because of the error logging which just hogs all the resources on the machine.
One option is to disable such logging completely for a given window of time and see if the machine hangs. If it does, then logging these messages is a secondary issue, indicating that the GPU (or firmware/drivers) are not handling conditions well and instead of giving up and crashing the driver, just unconditionally consume all available resources (bad idea).
Since the specific machine in question has two graphic cards, one crashing is not catastrophic.
NVidia - in general - has a bad track record in my book. For example,
http://support.apple.com/kb/TS2377 (this is still an on-going issue - 3+ years as of today). I have already had the logic-board replaced once for a different issue - which resulted in a new/refurbished GPU. 😟
Since this thread has originated in Jan 2009, I suspect, this issue
might just take as long to be acknowledged, and dealt with - as the 8600 issue mentioned in the support article.