Jumping the Shark
From a consumer perspective, Windows, and by extension, Microsoft, have now jumped the shark. Simple as that.
Sure, Microsoft still have the Xbox 360, which is much fun for the kids, but how many people (grown ups) are going to build an ecosystem around a 7 year old games console? Particularly when they already have iDevices and Droids in their pocket, or lying around the living room.
Microsoft have simply moved too late, and massively under-delivered.
Offering a single UI that spans the desktop, tablet and phone was a huge ask, but one they probably shouldn't have attempted as I'm not sure anyone really wants Metro (or whatever its called) on their mouse-driven desktop. Metro is instant alienation of those who are quite happy with their current hardware keyboard and mouse driven PC, and who struggle to get their head around the concept of a largely touch-centric desktop, when their screen doesn't support touch... it's a horrible compromise and one that wasn't worth making. As, indeed, Apple have not attempted, and for very good reason. Unlike Microsoft, Apple eschew compromises whenever possible.
As such, Windows 7 is probably the last Microsoft desktop OS I'll be installing and using at home. Not sure what will replace it, but it certainly won't be Windows 8 or what ever comes after it. Chances are it will be something Unix/Linux based, and maybe (hopefully) I won't even need a desktop in a couple more years, I'll just drop my multi-core ARM (or less likely, but still possibly, Intel) phone into a dock and have at it on a big screen with nice comfortable keyboard and mouse, moving windows around the desktop and basically feeling quite at home...