Personally, I kind of think we're in the waning days of Microsoft being able to sell their operating system for a hefty license fee like they have for years. One of the under-reported but to me, most interesting developments of the recent Consumer Electronics Show was the introduction of a number of Android Desktops. Now before you poo poo this just think that we're going to very soon be seeing 64bit intel chips running Android and that 64bit allows for increased memory access and thus the ability to run more complex programs.
Is the day far off before we're seeing photoshop and MS Office caliber apps available on our Android tablets/desktops? I think it's inevitable frankly. It's going to take some time...especially in enterprise corporate situations where security is a factor, but I can see 5 years from now most of us doing our work on Android and perhaps Chrome based machines. In fact I think the typical worker won't even need a Windows desktop anymore. You'll probably have one or two Windows workstations in an office for those really heavy duty programs that need it. For everyone else Android might be all we need to do our jobs.
Now what might happen is as Android starts encroaching on enterprise computing Microsoft is forced to do away with their fee structure in order to stay price competitive with Linux based OSes like Android. They might still make money from Office and support services. I think they'll sort of morph into an IBM like services model with Windows being less and less of their profit.