As of March 18th, Windows Vista SP1 was released to Windows Update. I have been waiting for this so my PC will maybe be faster after the update. I've installed the Beta SP1 at work a few weeks ago and it actually does seem dramatically faster. Here are a few things to know before upgrading to Windows Vista SP1:
1) You have not yet installed all the prerequisite packages you need for Windows Vista SP1.
To install them, visit the Windows Update control panel and click on "check for updates." Just so you know....this may take up to 1 hour to complete so do it at time when you are not busy.
2) You have a pre-release (or beta) version of SP1 and need to uninstall it before installing SP1.
If for some reason Windows Update does not show SP1, check out this list from Microsoft about Windows Vista SP1