Just a few hours remain before the retail launch of Vista, and many stores are getting ready for the expected explosion in purchases. Some are going so far as to opening their stores early, despite the fact that software is software and doesn't suffer from the supply-and-demand issues hardware can. Will initial sales really be that high? I doubt it, and instead think we'll see a more or less steady stream of upgrades over the next few months, as people wait until they see it in action or wait until they've used it at work.
Given the large number of people that participated in the beta, though, Microsoft will probably see much quicker adoption with Vista at the home-user level than with XP. If you remember the launch of XP, you remember confusion. I don't think that will be the case with Vista, despite its extra fluffiness.