The Nokia N800 Linux tablet looks very interesting as an ET platform. It could make a cool augcom device. High-functioning users could use the touch screen while children likely to throw things might use a web-cam based input mode. It looks like the camera can be pointed at the user, so the device could sit on the table out of reach with the camera focused on (say) a pad with colored regions in front of the user. Touching these regions could be the users "switches". With fairly loud sound and a not too small screen it might be usable. At $399 it is certainly cheap enough for experiments. Here is a nice video demonstrating some of its capabilities.