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Its my opinion that Windows 8 will alienate desktop and laptop users who do not have a touch screen. The Metro UI is perfect for a tablet and touch screen devices, but that's it. The fact that Windows 8 has Explorer seems more as an afterthought to keep those without a touchscreen happy, however it isn't very user friendly without the start button or orb. Removal of the start button really makes Explorer not worth keeping since now shortcuts for Explorer only apps will either need to be in folders on te desktop or on Metro which is difficult to manage with a keyboard and mouse.
Microsoft should have two different versions of Windows 8, or prompt at install if someone has a laptop or desktop without a touchscreen. If the customer chooses the version where they have a touch screen then have it boot to Metro. If they chose the version without a touchscreen it should boot to Explorer that has a Start button/orb and on the start menu have an option to enter Metro.
Basically make Windows and it's default GUI specific to the device it's being run on. This would make both desktop/laptop users happy since they won't be stuck with Metro by default, and it'll make tablet/touchscreen users happy as they have an interface built around Windows geared specifically for them.