One of my fellow MVPs forwarded a link to a post on the planned Vista SP1. This is supposedly already under the works and MS is looking at early TAP participants. I am not suprised, since I would have expected that as soon as Vista was RTMed (or near RTMed), the team would have started working on the SP and maybe a few on the next version of Windows too.
SP1 for Vista should be a easy go as quite a few technologies that were not fully completed, just did not RTM with Vista. So they would need a SP1 to get all of those out as soon as they are complete.