Originally Posted by Riocaz
One could argue that pen only systems are less usable. I certainly found that with the iLiad. However that may simply have been the iLiad's implementation.
I think a lot of it would have to do with the implementation and UI design. I would think you could design a UI such that a pen is used to trigger the screen performing the exact same functionality as a finger would. So, other than having to make sure you could find the pen, the interface could be identical.
Other than that, it may come down to a tradeoff. Either a layer under the screen, a DUO type sensor, or a finger touch screen. The first two may not be as intuitive to use, but the latter will reduce your contrast. It would come down to what was more important to the user.