I have worked corporate IT in two large organizations doing server administration. I can say with confidence that they will never go with Macs for general desktop use. They would go strictly Terminal Services first, for end users. FAR more cost effective and easier to manage.
Then there is the “change” factor. End users freak if their desktop icons change. I can only imagine informing 10,000 computer illiterate users that they will be required to learn a completely new OS.
Ahem....the proper term in "Lusers". =;^D
I think that's one of the reservations with Vista. There's a learning curve between XP and Vista GUIs, and if you're going to do that, you might as well get a better OS as well.