If you haven't updated to Vista SP1 yet, Microsoft has now started the process of sending it to you automatically via Windows Update - if you use the English, German, French, Spanish, or Japanese versions. The other language packs will be released to automatic distribution by mid-May.
Don't panic if you don't see Vista SP1 show up immediately. According to Chris Flores' announcement today at the Windows Vista Team Blog:
While we're beginning automatic distribution today, you might not see it right away since the distribution process is very gradual. As I called out on April 7th, we'll be distributing the service pack slowly so that we can help Windows users have a good experience.
On April 7th, he wrote:
We have a lot of Windows users, so not everyone will get it on the same day. In fact, it will go to a small percentage of Windows Vista users each day. The exact timing of when you will receive it depends on when your PC is ready for Windows Vista SP1.
Good question. A better question is, "have you made sure your system is ready for Vista SP1?"
Microsoft has made it very clear that a system with any one of eight problems won't be offered Vista SP1 automatically, either by Windows Update or its corporate sibling, Automatic Updates. We first discussed the causes and recommended solutions last month , but you should also consult the newly-updated version of Microsoft Knowledge Base article 948343 we cited.
Version 7.0 of this article adds additional causes and solutions:
If you've assured yourself that your system isn't on the "naughty list," what are your alternatives?
Need more help with getting ready for Vista SP1? See our extensive coverage.