For business, cautious, or cautious business users, upgrading their OS is nothing to be done on a Thursday night after work and forgotten about. For those people, it's going to be a smart idea to wait until Vista Service Pack 1 is released before switching from XP.
Not only is SP1 going to bring fixes, "Fiji" (the codename) is going to have OS components that missed the cutoff for release. Among them is Windows PowerShell, a command line shell more powerful than old timey "cmd".
As a refresher, Win XP took 11 months to release their SP1, which if Vista were to follow this timeline, would have its SP1 released in December. Undoubtedly, Microsoft will want an earlier release to lure the business cautious users into upgrading. For early adopters (like us), home users, and the adventurous, December is just too long to wait.
Vista Service Pack 1 is coming [APCMag]