As far as general consumer usage goes (internet, email, etc) this could just be a long lasting fad, and possibly even a permanent fixture from here on out as an added option to the electronics world.
On the other hand, I really cant see power users, gamers, or workplace professionals taking touch-screen technology in to the mainstream.
I think that the keyboard and mouse approach, no matter what they look like (trackball, ergonomic, small/compact form, etc...) will always be the primary demand for a computer just due to the functionality of both. I can't see engineers or CADD users doing all their work on a touchscreen, or even a voice input computer either.
Keyboard and mouse is just too solid of a design, and too near perfect for functionality.