This does not change my timetable. I will not approve Win7 for my clients until others have borne the slings and arrows of early adoption, giving us the benefit of their experiences.
From published reports, it appears that it will be easier to upgrade a Vista system to Win7 than an XP system to Win7. I'll provide some further guidance here once I understand the two processes better. This is a complicating factor that must be considered carefully, especially for larger deployments of Windows.
There is also some news indicating that Microsoft will offer a sort of "O/S Protection" policy - buy a Vista-equipped PC now and get a free or discounted upgrade to Win7 when it becomes available. Details are not yet available.
The bottom line here is that buying PCs with Vista Business now is okay, no matter when you plan to move to Windows 7.