Vista SP1 is out now and may be downloaded via automatic updates (not sure it might be manual only).
It took my Vista machine about 1 hour to download on broadband (434Meg) and about 3 hours to install so it takes a while.
After using it for a couple of hours it seems faster and no problems but it is very early days yet.
If you don't need it and do need your machine (I have other machines if this goes wrong) then leave it a while for others to find any potential problems.