Windows Vista Service Pack 1 was released to the public today. You can wait another month or longer to have Automatic Updates install it automatically, or you can use Windows Update to get it now. The service pack includes fixes for a number of security, reliability, and performance problems found since Vista's release.

If you're among the relatively small number of people for whom Windows Update doesn't list the service pack, this article from Microsoft explains why it may not be available. Most likely, you either have a device driver that isn't yet compatible with SP1, you have a language installed for which SP1 isn't yet available, or you need to install other updates required for SP1.