Well I upgraded my desktop to SP3 today, and things do not appear to have gone off without a hitch.
Doing a normal or safe-mode boot results in a stop code of c000021a. After digging around, and being relatively certain that the system doesn’t have some sort of virus infection, I found KB 156669. This does not appear to be the same issues as the endless reboots after SP3 (The endless rebooting is a symptom of the crash, not an indicator).
Booting the system into last know good configuration got me a workable system again, and I’m going to enable more logging and hopefully isolate what is going on, or if this is some sort of edge case on the SP3 install, and things will be running smoothly from here on… I will do a follow up post if I find something useful.
ASUS motherboard, Intel 4 CPU, Nvidia GeForce 8600 GT