Virtual touchscreens would make Windows 8 much easier to use.
Windows 8 is easy to use with a mouse or small touchscreen, but it would be much easier to use with larger screens if the touchscreen could be virtualized. That is, the screen area would be mapped to smaller area on another surface. A person's fingers would control cursors on the screen. This would keep people from having to reach out their arms. It also wouldn't require an expensive new monitor or cleaning off large screens.
There are two ways to virtualize a touchscreen:
1) Hover-sensing trackpads - The screen area is mapped to the trackpad area.
2) Motion sensing, like Kinect or Leap Motion - The screen area is mapped to an arbitrary rectangle on a flat surface.
Windows 8 with Modern UI has already surpassed OS X in terms of simplicity, and virtualizing touchscreens would make it even easier to use. Apple needs to simplify OS X and use virtual touchscreens also.