I am in agreement with your post- but that's a history lesson in the cut throat world of business- but I can see no software company poised to overtake Microsoft in the medium to long term.
What is the market share for Apple desktops/laptops 5-6% ? -I think that would include both business and consumer. There is no viable option for medium to large businesses unfortunately.
Even the cloud won't change this and to be fair, Microsoft is too far ahead with:
Identity management (FIM)
Collaboration (sharepoint, Team Foundation, Exchange 2010, Lync)
Infrastructure (SCCM, SCOM, Forefront Threat Management)
Windows 8 - same OS experience on multiple devices
Training (MSDN, TechNet, MVP, Virtual Labs)
Administrative languages like Powershell are much more powerful than Bash shell scripting.
Unless you can name the successor I'd say it remains in the eye of the beholder.
Apple's in roads over the last 10 years have all been in the consumer market- they're great gadgets - I have an iPhone and iPad but- there toys
IBM? - a relic
Google android/apps will take a share from exchange but office365 is on the up
RedHat/Fedora - Why?
MS would have to slip up big time, I'm talking two or three vista's in a row for any of the contenders to square up.
Yes you can point to things like Firefox, but a browser is One thing, complete enterprise infrastructure is entirely another.
You won't be deleting your AD account anytime soon
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