That's the news published today at Windows Vista Team Blog.
Today, you can now download Windows Vista SP1 via Windows Update. For those of you eager to receive the benefits of Windows Vista SP1 - you can now do so! We've seen quite a bit of questions in our comments so we want to communicate as much as possible surrounding Windows Vista SP1 and today's release to Windows Update as we can.
According to this site:
SP1 will start downloading to PCs automatically beginning in mid-April (Remember, this happens only if you have your Windows Update configured to automatically download updates and SP1 will automatically download but not automatically install). But if you want to get the benefit of a year's worth of improvements right now, go check Windows Update today...(Hit the Start Menu, All Programs, and select Windows Update).
I installed a few weeks ago in my Samsung Q1 and I felt the difference, I wont say that you should expect miracles but it helps. So far, I have not had any problems or issues so far.