Re: So, Windows is...
I helped an organisation do exactly that, successfully on more than one occasion. The trick is having a careful plan and giving it more than 2 weeks.
Our plan was to keep the existing Office software on the PC's for the time being, to open those legacy documents created on it but use LibreOffice to create all new documents and to open them. Most users were very happy with the arrangement and the company reduced it's IT spending over the next two years (and onwards). This paved the way to upgrade most of the departments to Linux two years later. Finance wouldn't budge because the crap software provided by banks for integrating with them, was only designed for windows.
The two companies I'm thinking of no longer need to buy antivirus products or software licenses. They also have reduced their desktop support staff, as no viruses to remove and operating systems simply don't need to be reloaded. The staff are more productive too. There is no rebooting of PC's in the middle of the working day anymore or waiting while updates are applied.
The support is done remotely now and therefore can be achieved on demand as no travelling required.
Since then, they have been spending their I.T. budget on nicer hardware, both out back and on the desktop, making the whole thing even more reliable. Best decision they ever made.
I use Linux at home and nothing could ever persuade me to go back to Windows (I recommend Ubuntu with KDE desktop).
If small organisations can plan this kind of migration, get it right, save money and increase productivity, why can't the US DOD?