On the whole “tablet will replace the PC someday” thing: no, not exactly. What will most likely happen is a central computing core will eventually be powerful enough to serve as a “tablet” as well as to be plugged into a suite of “PC” peripherals like a full sized keyboard, accurate pointing device, external storage, and full size monitors.
There will never come a time when all (or even most) of the functions people currently perform on a “PC” can adequately be performed on only a “tablet” minus some or all of those external peripherals. It’s not a matter of computing power, it’s a matter of how large the human interface devices need to be for us to comfortably use them. We can’t make people’s fingers smaller, nor their eyesight more acute, nor their ability to tap a screen within pixel-perfect precision more accurate. Even in a future scenario with holographic displays and gesture-based interfaces the human accuracy element is still there, and all of that (currently) science-fictional control stuff is still a suite of external interfaces, not actually part of a tablet. Even if you were to jump ahead further still and argue direct neural interfaces for input/output, those are still interfaces to biological peripherals present in our bodies.
At what point do you accept the semantics of what a “tablet” computer really is?
The marketplace is currently helping shake out just which computing activities are suited to a tablet interface, and which aren’t. Microsoft’s “Surface” is a big step towards recognizing and reacting to that shake out. There is still a long way to go.