These are just my opinions here, but I'm feeling a bit of deja vu here regarding Windows 8 and the new Microsoft Surface tablets.
The Surface reminds me of the Zune, which was a product line intended to compete directly with iTunes and the iPod. It made a bit of a splash, but never really caught on. Thing is, the Surface costs essentially the same as an iPad, and even though in fair disclosure I do not especially like Apple computing products, I think Apple's iOS user interface is way, way, WAY more usable than the fluorescent-pastel atrocity which is Windows 'Modern' (renamed from 'Metro' probably because of all the reviews out there from people saying they hate it).
And Windows 8 itself? Maybe it's quicker than Windows 7, but honestly, with an Intel SSD boost for my main hard drive, my boot time is only about 20 seconds anyway — and I have a fully customizeable UI that doesn't make my eyes want to bleed every time I look at it.
As I mentioned in another post, I beta tested Office 365, the successor to Office 2010 — and I hated it. All the visual cues and sharp contrast I was used to in Office 2010 (and 2007 and 2003) were gone, replaced with a washed-out low-contrast white-gray windowed interface that literally added time to my ability to locate frequently used functions.
Here's the thing that Apple recognized that Microsoft seems utterly oblivious about: Desktop/laptop work and touchscreen use are different. This should translate into different UI designs — which Apple has done and Microsoft has chosen to reject.
People working with a traditional computer and doing more than one thing at a time actually like and prefer multiple windows and a UI that makes it easy to locate and use frequently accessed applications and functions. There's lots more screen real estate available and a good UI will take advantage of it — especially for people with multiple monitors. You can take the icons and give them unique, identifiable shapes and labels.
Those using tablets have different needs and are usually doing just one thing at a time. There, if not for the inherent ugliness of color choices and user-antagonistic decision to make all the Metro 'tiles' look pretty much the same, the Win8 UI almost makes sense. But as others have already noted, there is much more you have to remember, such as where the hot-spots are on the screen so you can access functions.
Once more: So not an iPad fan here. I don't even own one. But I have friends who do own them, have had a chance to play with an iPad for several hours and generally liked the experience. My main barrier to entry is the expense and the fact I'd have to spend even more to come close to matching the application software base I've built up over the years for my Windows desktop systems.
While I don't think Windows 8 will be the disaster Microsoft BOB was, I do believe the comparisons with Vista are inevitable — only in this case, instead of Vista's well-documented functionality flaws, it's the human interaction and usability factors. Just as one anecdotal point of data, when Win 7 was coming out, I immediately began upgrading my Vista systems to it.
I have no such plan for Win 8.