At work definitely NOT. Too many process critical applications that would mean upgrading or changing every single system! that would be far far more costly than any savings obtained. Also we have open source that runs on windows.
At home almost definitely yes.
As we move to Web Applications that are served independently of each other directly to Browser clients which are agnostic to the Server software I can see us slowly buying from third parties applications that may run on the backend on this or building applications fully on those OS's. I hope this will just push MS prices down so all OS operating costs align effectively and makes it less of a competitive issue.
I specifically don't like the idea of FREE - we use QGIS at work basically for zero cost - I really want management to donate to the project - they almost definitely will not. At home I often buy more expensive tools for my shed for tasks that I consider particularly important.
At home SQL Server is already free (Developer edition), Windows is cheap, given the amount of time spent using it the cost for a pro version is roughly £0.35p a day in the first year which is peanuts, and after 3 years it's essentially free, not including the major updates we get each year now.