I was an intern on the windows user experience team last summer, so I saw a lot of this new ui. While I will never personally enjoy it (emacs is my ui), I'm proud of them for it and I think it will do well.

The first thing to remember is that you have seen very little of the os as a whole. You saw a "desktop" and some sample apps. There is a lot to come, and a big part of the experience will be determined by third-party developers, so try not to judge too harshly just yet.

Also, it is absolutely gorgeous. iOS looks like rocks after this. Big sharp clunky rocks. Sure, you can pinch and zoom and rotate with some fingers, but that's all at the app level in iOS. In windows 8 (from the video at least, I didn't play with it in such a mature form during my stint), everything is fluid and responsive, transitioning smoothly between actions, rather than closing one before opening the other. Where iOS enforces conformity between apps' ui and puts clear separation between them, windows 8 seems to let each app define itself, yet still be somewhat symbiotic with the os itself, and with other apps.

Why all the complaints about excel? Microsoft can't alienate enterprise, and I think we all know how much enterprise hates even UI changes. You aren't going to do real excel work on a tablet anyway (the most you'll do is scroll around and look at the figures someone emailed you), so why do you care if the ui sucks for tablet?

Most importantly, though, I'd like to examine one of Gruber's points:

The iPad succeeds because it has eliminated complexity, not because it has covered up the complexity of the Mac with a touch-based “shell”.

The iPad does eliminate complexity: this gives it an opportunity to break current notions of computing, and this helps users recontextualize the tablet and reintroduce themselves to it. In a way, it's a My First Post-PC Computer, designed to re-teach us about computers, as infants, to clear the way for better things to come.

Windows 8 might be that better thing, or at least the first real instantiation. I find that it seems extremely futuristic, in the sci-fi movie sense. It seems like the type of interface we've seen in movies about future societies where computers are embedded in everything, and they all interoperate seamlessly.

Notice the emphasis on home networking, and imagine your desktop, with all your pictures and movies, serving them through your house to your TV, your tablets, your kids' tablets, your picture frames. Your kitchen table runs the same browser as your desktop, and can access everything on your desktop, so you can pull up recipes that you bookmarked earlier that day. It also lets you know when you have to finish dinner so you can make the movie you scheduled. Your fridge knows what's stocked (and what's expired), and can send a message to your spouse's car asking them to pick up the ingredients you're missing for dinner tonight. Of course, when they get to the store, the cart recognizes them and loads up the list too.

Of course I've gone a little bit crazy there, but I'm sure you can see what I'm doing. Right now, we have (or, in about a year I guess we will have) two devices that interact in a way something like this. The only thing left to do then, is to scale up from 2 to 100. That's easy, the step from 1 to 2 is the hard part.

The point is that windows 8 looks to me like the first real step toward this goal, and the progress is happening exactly in the fact that it does not eliminate complexity, it does not segregate the tablet and the pc.

Why do you need to plug your iPad in to your Mac in order to do stuff with it (if this is not the case, sorry, I don't own one and my memory of being told this may be fabricated)? Because iOS doesn't have all the stuff in OS X that it needs to do things on its own. Your windows 8 tablet will have all that, so it can function on its own, but it also speaks exactly the same language as your windows 8 pc, so communication and cooperation between devices is trivial, even natural.

Of course, I still don't like microsoft, but I have to give them this one. They are absolutely killing it.