Microsoft has already indicated there is going to be a six week wait for Windows Vista SP1 because of driver issues. Even without that, they seem to have issues with just the prerequisite downloads for SP1.
In most cases, they reported that the final update hung while displaying the message "Configuring Updates Step 3 of 3 - 0% Complete," which was followed by a reboot of the PC. Which was followed by another reboot, and another. "[It] reboots ad infinitum," said Frank Melk on the Microsoft support newsgroup. A smaller number reported a different problem: After the update, their computer refused to boot normally.
Messages left on the newsgroup indicate that Microsoft is aware of the problem. Someone identified as Darrell Gorter, who claimed to be with the company, asked users to send him log files "to determine a cause for the issue." Official company representatives, however, were not available Sunday for comment or confirmation.
Microsoft appears to need ALL of those six weeks.