Would you be happy with a tablet computer as your main machine? If it were powerful enough, I'd say yes. I expect I would a least have a dock with a real keyboard on my desk though. The biggest problem I can imagine is screen space. Tablets just don't have the room to move that I need for my work.
I think, at some point in the future, the power of phones will have increased to such a degree that they are our primary computing devices. When we want to use them at home, we'll have docks with standard connections that we can drop them into, from which they will power desktop screens and full-size keyboards.
Mokalus of Borg
PS - Or maybe most of our software will change to match small screens and touch.
PPS - A lot of it is changing that way already.