I do think Bill Gates was on to something. From a UI perspective, a pen/touch screen is superior in that it removes one level of indirection in a UI paradigm that is attempting to be "direct manipulation".
However, for this to be the most popular form of PC, I think there will need to be a breakthrough in text input. I've looked at a lot of alternative text input techniques and I don't think any of the current ones will cut it. This includes soft keyboards, crazy dasher-like things, predictive stuff, handwriting recognition, gestures, voice, etc. The huge advantage of keyboard entry is not only the tactile feedback, but that it has a fairly low cognitive cost. In other words, you can think about other things while you type - it's automatic. Pretty much anything aural or visual will take away from thinking about your real tasks.
However, for this to be the most popular form of PC, I think there will need to be a breakthrough in text input. I've looked at a lot of alternative text input techniques and I don't think any of the current ones will cut it. This includes soft keyboards, crazy dasher-like things, predictive stuff, handwriting recognition, gestures, voice, etc. The huge advantage of keyboard entry is not only the tactile feedback, but that it has a fairly low cognitive cost. In other words, you can think about other things while you type - it's automatic. Pretty much anything aural or visual will take away from thinking about your real tasks.