BTW, I've upgraded 4 machines now and not a hitch with any one of them. This update takes a while to complete (which is unsurprising since MS calls it pretty much an "OS replacement" for Windows) but has been going perfectly smoothly and the end result has been as good as they get.
As I'm touching client computers for other things I'm kicking this update off at the end since I'd rather get this ball rolling while I'm there to see if it looks like anything will go wrong. I'm more than willing to walk away now once things get to the "Blue Screen of Progress" stage. I just warn them that when they first log in again after the upgrade, it will appear as though the computer just came out of the box and you get the, "Hi . . . We're setting a few things up for you," sequence because it is a major upgrade.