Sorry to necro a thread that has not seen a reply for a few days, but thought I would chime in here.
I've been running Windows 8 on my desktop off and on since it first hit Consumer Preview in Feb of last year; and had my full retail copy of Win 8 Pro on the first day of general availability.
The os is not perfect by any standards(what software product ever is), it has some bad things going against it, and some good things going for it.
Firstly I still have not grown to fully accept its Metro interface as of yet. I can navigate it easily with the mouse, and have most of the more useful keyboard shortcuts figured out. The interface to me is Win 8's biggest drawback, I like the traditional start menu better. That being said there are programs like Star8 that will give you the real start menu back.
Most of the changes that really make a difference in Win 8 are under the hood, and not readily apparent to the end user unless you run around with a stop watch. Startup and shutdown times are significantly improved, the USB sub system appears to have had a major overhaul resulting in improved file copies with more accurate estimations of completion. Hyper-V, which is the Microsoft software stack for creating and running virtual machines is included with the Pro version(Though you must have a Core i7 or newer cpu to use it). As well as DirectX 11.1 being included out of the box; Nvidia does not yet fully support 11.1, ATI claims full 11.1 support at this time.
As to the idea of the OS having no effect on game performance, rewind to the Windows Vista launch; nuff said
Windows 8 in my opinion takes the stable foundation Win 7 offered, and adds more to it. Though Metro really is almost more of a drawback than its worth.
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