If you're a consumer, you use the Metro UI.
If you're a producer, you use the Desktop.
The line between "consumer" and "producer" is so fuzzy that this doesn't sound feasible to me. [For the record, I haven't used Windows 8 yet.]
Both "types" of users—if we assume for argument's sake that such a distinction can even be made—tend to use a number of apps; each of those individual apps falls somewhere on a continuum of consumption vs. production. And even where each app falls on that continuum for that person may vary throughout the day!
I expect there will continue to be tablets — and they should have tablet UIs — and there will continue to be "desktops" — and they should have desktop UIs. They should be made similar in aspects where it makes sense, kept different in those aspects where it doesn't, and there should definitely be many apps that run on both (with appropriately varying UIs depending on platform) and which constantly sync so that the users' production and consumption can flow between them as desired.
If Microsoft pulls off a single system (even with two modes) that can transition without confusion and frustration between the two and that doesn't heavily compromise either one, then they'll have a very unique offering. But I don't think it's clear that such a goal is even achievable.
> If you're a consumer, you use the Metro UI. \ If you're a producer, you use the Desktop.
The problem with this is that the "new" desktop is fundamentally different from the old one. It's not as simple as saying "oh, just use the desktop".
> IMO, they are insistent on improving their products.
I wouldn't consider presenting users with a puzzle to be an improvement. I can pick up my iPad and instantly figure it out. I can pick up a MacBook Air with iOS-like features and instantly understand how they work. I was stunned at how much effort was required to learn Windows 8. Absolutely stunned. How exactly is that an improvement?
By the same token, I can pick up a Windows Phone 7 device and instantly understand how to use it - but Windows 8 still somehow turned out to be a confusing mess with a mouse/keyboard. Even on a touchscreen device - it's not completely clear how things work. It was as confusing to use as a Blackberry Playbook.
> The problem with this is that the "new" desktop is fundamentally different from the old one.
If you can't figure out how to use the desktop without the start button (by going to the left-right sides with a mouse movement that is even easier to do), then you really should be using the Metro UI instead, because it was made exactly for you.
> I can pick up my iPad and instantly figure it out.
1. When I got my iPad it enraged me to learn/figure-out that I had to install iTunes and connect the two.
2. You're now comparing the touch based iPad UI with mouse/keyboard driven Windows 8 Desktop UI.
1. You don't need a compute to use an iPad anymore.
2. It doesn't matter if it's apples-to-oranges as far as touch vs. mouse/keyboard - the key issue here is how understandable the UI is. Windows 7, if you know how to use a mouse and a keyboard, is completely understandable. Windows 8 makes absolutely no sense.
From what I can tell everyone is going to have to use the Metro UI because it has replaced the Start menu as the built-in launcher. There is also a new menu on the right side of the screen that let's you access search and settings among other things. So even producers must use some of the Metro UI on a daily basis.
I predict we will see a number of utilities emerge in the next few months to emulate the Start menu or otherwise provide alternatives to the Metro UI for said tasks.