Every once in a wile, you can lose a window way off the edge of a screen (particularly if you swap between multi-monitor setups often). If this happens, you can use one of Windows 8's new full-screen apps to get it back.
Simply launch any full-screen Windows 8 app (Microsoft bundles a bunch, so you shouldn't have a problem finding one) and then snap it to the side of the screen. Once you go back to the desktop, you'll see that any apps off that edge of the screen have been relocated back into view.
Finally, you have a reason to use a "Modern UI" app!