Remember that issue where trying to install Vista SP1 would result in a hard-to-break reboot cycle? Well, the Microsoft Update blog says the problem was caused by "a few unknown and rare events" during the installation of one of the prerequisites to installing SP1: KB937287, the Servicing Stack Update (SSU). That issue is reportedly fixed now:
To address this problem for people who have not already installed the SSU, we are releasing a fix tomorrow which will install prior to the SP1 Servicing Stack Update. This pre-SSU update helps to ensure a smooth install of the SSU by working to prevent the system from rebooting during the SP1 SSU installation. We also made additional changes to the SSU installer code, so that it checks for and requires the pre-SSU (KB949939) before it will install.
These two updates should now install seamlessly through Windows Update, in the proper order, so those of you with WU set to “install updates automatically” who haven’t already installed the SSU don’t have to take any further action. For those using the standalone download of SP1, the issues we encountered do not affect that method of installing at all.
Additional information in the announcement indicates that this issue doesn’t affect updates using the standalone installer.
If you've been holding off on SP1 deployment because of this issue, you may now resume.