So this isn't something I'd heard of yet, but I just stumbled onto this writing emails and playing Sleeping Dogs.
So right now I've got my two 27" monitors going. Monitor 1: Desktop, Sleeping Dogs in windowed mode by maximized. Monitor 2: 2/3 Desktop with VLC playing, 1/3 mail client. I'm playing Sleeping Dogs with a game pad on monitor 1, see an email come up on the Windows Modern UI mail client. Move my mouse over there without even thinking and start typing. I didn't even think to move my mouse back over to Sleeping Dogs and click on the window to focus and just picked up the game pad. Still worked. When I realized what I'd done, I open up a new email and started typing while controlling Sleeping Dogs at the same time.
It works with other Modern UI apps too. I can browse in Chrome or IE10 while playing games with a gamepad. It's kind of small, but if office in the metro side is decent, I can see working on office stuff while a kid plays a game on the desktop on another monitor.
Edit:This happens even with windows on the desktop too. This didn't work in Win 7, so... new Windows gamepad feature?
That sounds interesting, definitely handy for multi-monitor setups.
That actually is something that would make me upgrade. I use either 2 or 3 monitors so that would be incredibly useful for when I'm playing games.