But what about all the rest of the computers? You know, those big things on your desktop? We all know just how smart most users are when it comes to figuring out how to use stuff on a computer. Its taken years to get to the point where your typical "user" can use a computer without too much difficulty. Part of this is due to the consistency of the Windows UI; folder windows, mouse motions, menubars, etc. Suddenly, we're going to throw something completely new at them, something which:
1) Has been shown to be difficult to do well for everyday use (touchscreen desktops)
2) Has a moderately non-intuitive interface (hidden UI elements until I swipe from a particular side, or maybe tap over here and here and here)
3) Has questionable benefits in a desktop computing environment where a keyboard is a perfectly appropriate device
And, once they learn all that, our user realizes that he still has to use the original UI for many programs! That's right, photoshop isn't going to be going Metro anytime soon, and neither is Matlab, or Autocad, or Excel, or video editing software, or any "Pro" program (for lack of a better word). Metro may be wonderful for tablets and other mobile devices, but it sure looks like it's going to be a drag in being forcibly married to the traditional Windows UI.