[CONFIRMED] Smartglass will function as a game controller and second screen.

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JWeinCom said:
That'll be a useful feature if you have a smartphone with buttons. Xperia Play sales will go through the roof!

Microsoft has a patent for a "Controller" layout for a tablet or smartphone using touch.

Not all game types would use it.  An FPS, for example, wouldn't.  Not for playing the main game, for sure.  But puzzle games, certainly could allow for both the Xbox One wireless controller, Kinect, or Smartglass.