My ideal PC would look like a a Lego (C) (TM) (etc.) base plate, only taller so that it would fit the components. So that's what, a square 10"/15" or so on a side, gray plastic. There would be a collection of USB2 (and 3 if that's present) ports in or near the center of it, which you could then extend via a cable to whatever you felt like building at the moment.
So one day your PC might be a lego castle where you plug your iPod into a port above the drawbridge. The next day maybe you replace that with a pirate ship, and then the next day you go with a classic moon base.
The biggest coup of course would be to build the Lego Deathstar on top of it. (The USB cables would plug into the exhaust shaft, of course.)
This all accomplishes a couple of things: An easily transportable PC, with the potential for true awesomeness while keeping the flexibility of being very easy to change.
Search your feelings... you know this to be rad. 8-)