InfinitTouch has a new product on the market that represents a completely new approach to touch screens. The technology is called 'force panel' and product brand is InfiniTouch. Force panel improves upon existing capacitive or resistive screens with a more durable, vandal-proof construction and more design options available including integrating metal, wood or plastic into the touch sensitive surface.
The force sensors are located near the corners of the touch screen. Each force sensors detects different force according to a touch position. This differences are used to identify the exact location of the touch point (See their web site and technical document).
From the technical point of view, I guess it is difficult, if not impossible, to measure multiple touch points simultaneously.
See also their videos.