Really cool toy but there are some major drawbacks. So I still think there's plenty of uses for a mouse left.
If you haven't read the comments, here's the inventor:
http://mrl.nyu.edu/~jhan/
The image is back projected on an acrylic plate. This plate is illuminated with IR from the side. When you touch it, you break the total internal reflection, and your finger is lit up as seen from a webcam on the back side.
Because of the back projection it gets bulky and expensive. The actual touch sensing is cheap though. Well, apart from the extra PC that is dedicatd to extracting information from the webcam. But that might be possible to do on the same PC as the application is running on.
Because of the webcam, it's pretty low-res. 0.1" on a 36"x27" screen. But a finger is a rather blunt pointer anyway. So you can't make it much better unless you introduce a "mouse pointer" on screen, that you control with your finger just below it. But that will go away from the the intuitive "click directly with your fingers"-interface. Because you would need to first touch the screen slightly to see where it puts the pointer, and then (after fine adjusting) press a bit harder to perform the click. And you wouldn't put your finger directly at the point you want to click.
Then there's of course more problems
* Your hands/arms are in the way.
* You're greasing up the screen.
* It's hard to make an arm rest.
* It's best for ergonomy to work with you hands on a close to horizontal surface, but you get the best view of a large display if it's close to vertical.
So basically a really cool toy. But it could be useful for some applications where you don't need to click at stuff with high precision. A mixer table do come in mind as a place where it could be useful.
Now give me a second mouse.