I just received my HPWC, and will have it installed next week. They are (supposedly) being shipped out in order based on reservation number...I was P2009 and received my car on 12/30/12, in case you're wondering where along the line yours (theoretically) is.
At quick glance, the HPWC unit itself is about 6.25" wide by 15" high. The cable is substantially thicker than the portable charging cable that the car comes with: The portable charging cable is 9/16" thick...The HPWC cable is 7/8" thick, and is harder and less flexible. The charging stick is virtually the same as on the portable charger.
My HPWC came with a steel mounting back-plate, and a box with some screws, nuts, and a ground wire. That's it. No garden hose-style organizing hook, I guess that is still forthcoming. In the meantime, I will most likely use an actual garden hose organizer hook.
For those of you still waiting for yours, let me know if you have any questions about the unit.