Ever try to teach a business systems analyst how to traverse around inside a Unix box? From my limited experience, it’s like teaching a stroke victim to walk again. Because most got their literacy from PCs, whatever demands their administration’s going to need to be windows based.
Unix had made great inroads from mainframes into healthcare when I worked in it in the late 90 (with Ernst & Young in LA), but I didn’t see it moving into an environment dominated by Microsoft.
Linux desktops aren't as good as XP, and they do take some getting used to. If your end user just uses one app plus email, this is acceptable, but don't confuse general XP friendliness with that of Linux.
On the other hand, the Linux server stuff rocks. And, what end user cares what is going on in the server room, so long as it works well?