[Update 2: See here for more details on the console and tablet hardware, including many more photos.]
[Update: We now have a scant few additional details straight from Nintendo, as well as a few images in the gallery.
In single-player games, the tablet controller can display a completely different screen from what the TV is showing, and thanks to the tablet's gyroscope, the information on its 6.2-inch screen can change based on its orientation. In multiplayer games, the new controller can offer a player "a different experience" from the people watching the TV.
Nintendo has not released hardware specifications at this time, but has given some information on what the tablet contains: an accelerometer, a gyroscope, rumble functionality, a front-facing camera, a microphone, and speakers. Its button configuration resembles that of the Wii's Classic Controller: two analog Circle Pads, a D-pad, A/B/X/Y buttons, L/R buttons and ZL/ZR triggers.
The Wii U can output up to 1080p video via HDMI, and it can handle one tablet controller plus as many as four Wii Remotes or Wii Remote Plus wands. (In fact, the Wii U is backward compatible with all Wii games and accessories.)]
"A system we will all enjoy together, but made just for you."
Project Café's official name has been revealed as the "Wii U," which comes with a new tablet controller that includes a front-facing camera. Reggie explained that idea behind the console's title is to emphasize how players can play together, or stream content straight to a screen on the controller. The tablet controller will also be able to act as a separate 6.2-inch screen from your television, make video calls, browse the Internet, stream content such as photos and videos back to the TV, and interact with the Wii remote (with which the console is also compatible).
The Wii U will be arriving in 2012.