I'm having SP3 issues. It seems to install fine, prompts me to reboot, windows loads, etc. But towards the end of my Windows startup my Zone Alarm firewall/antivirus security suite starts up and hangs the system. A ZA alert pops up asking me to approve access for tlnt.svr, but the ZA window where I would click "approve" is unresponsive. If I ctrl-alt-del the system to shut down ZA, the task manager appears, but all of its buttons are unresponsive (i.e. I'll try to select a task, or something, and the window will say "not responding"). If I try to shut down the system it just hangs indefinitely. I can still move the mouse after hitting shut down, but any time I try to start a program after that point I get a system error saying the program can't load because Windows is shutting down.
I did manage to start Windows in Safe Mode and disable zone alarm. Then, when booting normally, Windows worked just fine. However, when I manually loaded zone alarm, the above problem repeated itself. I've browsed around for ZA/SP3 compatibility issues, but have found nothing (I have the lastest ZA, supposedly SP3 compatible), so for now I'm restoring to SP2, and am going to hold off on SP3 until I can find more information about this issue.