When I first came across the HP TouchSmart, I thought it was just a cool all-in-one with a touchscreen display. But what makes the TouchSmart really unique is that it uses cameras to detect finger touches, as described in this great NY Times article. The only other touchscreens (I know of) that use cameras are big ticket multi-touch systems like Microsoft's Surface, and Perceptive Pixel's huge interactive wall, which use cameras mounted behind the screen to "see" touches. The HP TouchSmart has two cameras on the outside of the screen in each of the upper corners. This allows the TouchSmart to use a conventional LCD screen instead of rear projection and maintain its slim profile. Since finding this out I've started to wonder if the HP TouchSmart may be able to detect multiple finger touches with some modification.