On Iwata Ask web site you can find some naughty photos of Wii U - maybe "she" will not be 2012 playmate but looks interesting.
On Kotaku there are also few inside photos.
On first look Wii U is very similar to Wii. Heatsink is twice bigger, fan is an inch or little bit more bigger also.
Wonder how Wii U will emulate gamecube mode - only by new CPU?