For those of you that experienced installation issues with Vista Service Pack 1, Microsoft has issued an update meant to fix just that. The updated installer is merely to adjust any issue with actually getting the update on the system, so for anyone that already has successfully installed SP1, you have nothing to worry about.
The problem lied with the Servicing Stack Update where it checked to make sure no other updates or installs were pending. Under certain scenarios there were cases in which it would always assume a reboot was needed first - even upon a fresh restart - prompting a reboot loop and a frustrated customer. This problem didn't affect everyone and the blog entry states that most people can just leave their machine to automatically update as normal.