Tablet users, I imagine, will stay pretty much entirely in Metro. It's just right for touch-based interaction on a small screen. But desktop users will be just the opposite: you might look at the weather app in Metro, or use the Metro calendar, or maybe check your email (though the email app has some issues; read more below in the "apps" section), but I can't imagine a desktop user wanting to use, say, a Twitter or instant-message app in Metro. For one thing, you'd have to keep leaping between your desktop and Metro, which is kind of jarring (Alt-Tab includes both Metro and regular windows apps)--even more than heavily using widgets on Mac OS or gadgets in Windows 7, and those are nowhere near as involved as Metro apps. For another, Metro apps are designed to be super lightweight and speedy and simple. That's fine for some stuff, but the email app is basically a touchscreen email app--if I'm using a desktop computer, with a keyboard and mouse and an ugly black tower filled with space-age components, why wouldn't I just use an email app like Thunderbird, or even a web-based client like Gmail, both of which are more powerful, flexible, and better suited for keyboard-and-mouse use than Metro's email app?