If it ain't broke, don't break it
The prospect of sitting at a machine for 'way too much time, installing expensive software only to wind up with something that doesn't even work as well as it did before, is certainly one of the reasons that operating systems like Vista just don't get the kind of retail buzz that they used to receive. Heck, I'm really looking forward to Apple's forthcoming OS X 10.5 "Leopard" release, but I'm also holding off on replacing an aging G4 PowerBook with a much faster MacBook Pro until I can buy a package that I know has Leopard ready to roll.
For developers and consumers alike, what's needed is plenty of discipline in knowing what's being changed, how it's being changed, why it's being changed, and how it might go bad. It seems to me that these days, the bulk of new software distributions are replacements for something else that currently works OK, not salvation from a primal state of softwarelessness: Treating users like established customers, not like breathlessly waiting newbies, is part of the overdue maturation of this business.