Many of you must have already manually downloaded and installed Vista SP1 when it was made from the Microsoft Download Center or Windows Update. Since April 23rd, automatic distribution of SP1 in English, French, German, Spanish, and Japanese (Wave 0 languages) has begun. So this means PCs that have automatic updates turned on and running the above language will receive via Windows Update. Automatic distribution will only occur, according to user settings, on PCs ready for SP1.
SP1 of remaining languages is already available for manual install on the Microsoft Download Center and Windows Update. Automatic distribution of those languages will start sometime in mid-May.
If you haven't yet installed SP1, I'll advise you to do so to see better performance, reliability and compatibility overall. Also, if you are an enterprise customer and want to postpone automatic delivery of SP1 in your organisation then Microsoft has provided a free Windows Service Pack Blocker Toolkit about which I had posted earlier,Windows Service Pack Blocker Tool Kit