“Microsoft was using a shallow pool as the “attract mode”, and the screen image looks and behaves like water, in a graphical way. Touch the surface with your finger, and it sends out realistic-looking ripples. But you can also put your whole arm across the surface, like a barrier, so there are ripples on one side and not on the other. Or you can use a book, or other object. It doesn’t require skin.
In fact, although the Surface is touch-driven, it doesn’t actually use touch at all. It uses infra-red photography. It can “see” things that are still above the surface of the 30-inch screen, so if you touch it, it knows which side you’re sitting. And although it does a brilliant impression of being pressure sensitive, it isn’t: it just works on the fact that your finger contact area increases as you press harder.”
Jack Schofield of The Guardian has published a nice short story about the user experience of interacting with the Microsoft surface: