Windows Vista Service Pack 1 has been released for general distribution.
Because of the size of the update (the download version of the 32-bit update is 434MB) it will be released on a staggered schedule to Windows Update users. In other words, you may not see any updates available if you go check Windows Update manually. This is what happened to me on one of my Vista systems when I checked yesterday.
I decided to download SP1 myself. Here’s the download page for the 32-bit version, supporting English (US), French, German, Japanese, or Spanish (Traditional).
The release notes are fairly Spartan. The only noteworthy issue in them is for the Business, Enterprise, and Ultimate editions: the GPMC (Group Policy Management Console) is removed from Vista when the service pack is installed. This has been discussed elsewhere. A downloadable replacement will be available eventually at this page.