Paul Thurrott updated his Windows Vista Service Pack 1 (SP1) FAQ

While most Windows service packs are hardly worth discussing, Windows Vista Service Pack 1 (SP1) has been steeped in mystery almost since before Vista itself was completed. With Vista, Microsoft has engineered a new update deployment technology that allows administrators and power users to "slipstream" service packs and other fixes into new Vista installations in a manner that is much simpler than with previous Windows versions. But the real issue with SP1 is in how Microsoft is handling--or mishandling, in my opinion--the dissemination of information about this release. For this reason, and because there are so many silly rumors floating around, I've created a FAQ for Vista SP1 that will be updated as new information is released. If it's not in this FAQ, it's just speculation.

Windows Vista Service Pack 1 (SP1) FAQ