Windows 7 works fine, at least in the limited capacity in which I have used it. It was preinstalled on my work computer. I may be buying a new computer soon, so I'll find out more. I've heard nothing but good about it.
Windows 8, however, looks like the Windows Phone 7, which was made to be simple yet powerful...for cell phones. While WP7 is a great system, I don't want simple for my desktop...I rather enjoy my relentlessly convoluted PC. They're going for a single, full-featured OS that successfully scales down from PC to tablets and cell phones. This means writing a system from the ground up that accommodates ARM processors, the architecture that powers those smaller devices, which happen to comprise the largest growth segment of digital devices. Therefore it's imperative that Microsoft enter the domain with a unified platform if they are to defend their long-term dominance over the PC market and assert themselves in the mobile arena.
Hopefully, the PC shell will not be limited to live tiles. I see tablet computing is a fad that will soon peak and then level off as its own field of computing. There will, until implantable interfaces are developed, always be a need for the desktop machine. The two fields are distinct, and blurring the line to this degree might just alienate the powet- and enterprise user.
*EDIT: I just noticed where they're packing Win7 in there for compatibility. That's a relief, but how bloated will this mofo be?