Materdaddy wrote:Not sure about a nintendo DS, but an iPod touch uses a completely different type of touch screen. It's glass, and completely different technology.
The iPod Touch (and iPhone) use a completely different technology. Your fingernail or a random little plastic stylus won't in fact work on it (I've observed Treo owners struggling with this). Your figertip or a specially-made stylus will. Different contacts with the screen register as separate contacts on the input (this enables multitouch). So yes, it's an utterly different input technology. This fact shouldn't matter to typical end-users, though. Most won't care about this detail. I know my wife and mother-in-law wouldn't.
The Nintendo DS, Palm 3, Sony MagicLink, and General Magic DataRover use the same basic technology as the Chumby. A stylus gives the best results, then a fingernail. Different contacts on the screen are averaged, so if you touch two points that are far from each other it should register as one point at the midpoint between those. The pad of your finger can work, but is considerably less accurate and it can be problematic to do drag operations with it.
The eMate (and other Newton-based devices) uses a modified version of the same basic technology as a Chumby. Not only does it have the pressure-sensitivity, there's a layer of very very small beads in between layers of the sensor, so that pressure that's spread over too wide an area won't easily get through -- you have to push the beads apart to make the sensors kick in. So a stylus or fingernail with a small enough contact area works with extremely high precision, and for the most part a fingertip pad won't work at all, not even inaccurately.
In terms of modern "casual user" expectations, the iPod Touch (or iPhone, same tech) and Nintendo DS are probably all that it's worth considering. It's very natural for large sets of naive users to compare any touch screen to one or the other of these, and in both cases, using the device naturally with your fingertip does not result in any visible warping of the display, even without any training. (I ran the other, monochrome device tests to satisfy my own curiosity, to most regular people they'll seem as exotic as my VirtualBoy does.)