SW,
It despends on what you call non critical. File, Auth, Mail, Print is windows and will be that for a good long while but is your source control server non critical? are your web servers non critical?
As a fellow MCSE might I recommend Red Hats training its far better than the Linux+ stuff..
I may do that eventually, but I have a free test voucher from CompTIA, and I picked up the courseware on Amazon for dirt cheap. I haven't really played with Fedora much, but 80% of the Linux-heads I know swear by it.
Most of the non-critical stuff I'm seeing are things like network monitoring, Linux desktops loaded with OpenOffice for lower level employees, and things of this nature. Web servers are definitely ripe for the Linux pickings though. Sleek and secure when compared to Server 2003 Web Edition.