I upgraded to 8.1 from Win7 last week. My first experience trying to compare a PDF document with text file in another editor was quite unpleasant (Metro essentially makes apps modal, which is nuts).
This is the biggest issue with window management on all new/mobile platforms, they can run multiple apps simultaneously but they can not run multiple instances of the same app! Compare the weather in two cities using the weather app, forget it. Compare two PDF documents with the office app, forget it. Compare two bus routes with your local public transport app, forget it. Why are we creating systems that are worse than what we already have.
Windows 8.1 can run multiple instances/windows of the same app, although the app needs to opt-in to implement support (which the built-in PDF reader, IE and mail client all do).
That's where the grandparent's idea of being able to run Don't-Call-it-Metro apps in a windowed mode comes into play.
Doesn't seem like it should be hard for Microsoft to accomplish. Metro's already supposed to be resolution-independent, so all that's really accomplished by forcing them to be fullscreen on desktop monitors is keeping ease of task switching and information density to an absolute minimum.
I upgraded to 8.1 from Win7 last week. My first experience trying to compare a PDF document with text file in another editor was quite unpleasant (Metro essentially makes apps modal, which is nuts).