What defines the PC for ordinary consumers is not the big black box under the desk, though. It's the keyboard, the mouse, the displays.

The smartphone may replace the box, but it won't replace the peripherals. Those will continue to be extremely desireable features for many tasks, because they are far more ergonomic and speed up many types of work.

I predict a smartphone docking station on every desk within 5 years, both at home and at work. Maybe a docking station on every couch, too, tablet form-factor.