@Ben Holmes
"...in most enterprises, the cost of redploying to kit, and retraining staff precludes any sort of move to an entirely different platform at all."
I can't count the times I've had a user ask me if/when we are getting any Mac's. The only retraining problems you are going to have are from the Luddites and I classify that as any one born prior to 1978. I fall into that range, but I have The Knack, so new tech doesn't scare the willies out of me.
Speaking of retraining... Most of the users do not care what OS the program runs on. They just care that it runs. If you are referring to retraining them on on the program that just replaced the one that runs on an MS OS, then yes, your are going to have some push back. Now think about that for a minute, especially if you were witness to the 'upgrade' from Office '03 to '07. Did the users flip out because of that fscking Office Ribbon nonsense? Mine sure did. Did that cause us to roll back the changes? No. Are they used to it now? Yes. Would they have been able to handle a change to say Ubuntu running (at that time) Open Office? Maybe. And I say that because the OS change would have been what got there attention more than Open Office. Why? Open Office, at that time, had a similar look and feel that Office '03 did. Most of my users have one or two in there group that can help train the others, so most of the time a change in product, or even a new product, is handled quite well.
You sound like someone that benefits from keeping a company from changing to FOSS by making sure that the CFO/CIO/CTO hears enough FUD to keep the licensing machine rolling.