Windows 8: A First Look
Sharing Among Apps
The Share menu lets you do just that. If you're running a conventional Windows application, you only have the choice to share a screenshot of the app. The same goes for Metro apps that don't have sharing functions, as shown here. There is a great incentive to have Metro-native apps, though.
That's touch integration and the ability to view apps full-screen – in so-called "lean-back" mode. A version of Microsoft Office for Metro is reportedly on the way.