This will seem ludicrous to most of you, but it appears that the problem may be solved by disabling GLX. I commented out the GLX module in my XF86Config and it hasn't frozen in 40+ hours now.
Of course, that means you have no 3d acceleration, which for most completely defeats the purpose of using the closed-source driver. For me however, I need it for TwinView.
So *ahem*, we haven't heard anything about this issue in over a month from nvidia (are you out there, Andy?)