None of the above...
They do not have the processing power, memory, storage or connectivity to make a decent rig. They are designed to surf the internet, watch movies, and text your buddies.
They might make a neat remote control for your real computer, and be handy for presentations to clients though...
There's an intrinsic issue with touch screen devices -- our hands were not designed to interact with them. Pushing a button is easy, but try moving your finger in a circle, or scrolling. You lose the ability of precise motor control, because of the friction on the surface of the screen.
Human nature is to control things -- that's why mice, keyboards, controllers, etc. are fairly popular.
Until somebody can overcome that distinct feel -- I don't see them as anymore than a neat looking remote control...