I think Android will never be anything more than a device for your tablet, phone, and maybe Google TV if that ever gets rolling correctly. Android is a multipurpose OS, but it's not as functional and fluid as Windows or OSX. Also, it doesn't help that it's built from Linux. There are great Linux OSes, but then there are a bunch that are terrible.
Windows, you have one OS every couple of years. OSX, you have a new update every year or close to that. The thing is, they're the same OS or relatively close to it as can be. Win 8 merges touch with desktop. OSX is merging ideas from iOS, but changing it drastically as Microsoft did.
I feel like MS' idea is brilliant. It's merging mobility with reliability and functionality. I realize the Modern UI on Win 8 lacks features in their applications, but you still have your desktop for work arounds. I know there shouldn't be work arounds. I have faith that MS will update Win 8 with a service pack or whatever they're going to call it eventually and correct the problems/things that truly need corrected.
While I like Apple's approach by just merging certain aspects of their ideas from iOS to OSX, I think it's a slow, meticulous process they're going through to get iOS to replace OSX as their be-all OS just like MS is doing. I would have liked Windows 8 to be Windows 7 with bits of Modern UI in it, but I understand where MS' thought process came from seeing as how they needed to act quickly to get back on track.
IMO, in the next several years we're going to see it as Windows > OSX/iOS > Android.