Not to involve heavy Microsoft bashing, but the biggest problems with Microsoft-based machines in critical or semi-critical roles on your network is that your hands are literally tied with respect to solving any security problems on those machines. Not only can you a) fix them if technical or b) hire a third party to fix them, in most situations you cannot even legally report them.
This is why Bob Toxen mentions this here, just because something has a seemingly easy to use interface does not provide ample argument against security concerns.
