Demonstration of the Mii channel on the Wii: http://www.gametrailers.com/player.p...pe=wmv&pl=game. Basically you can create a customized 3-d avatar to use in games like Wii sports. Demo complete with Samuel L. Jackson awesomeness.
The dude makes a pretty shitty Sam though. That aside, I love the concept. I'm gonna spend hours when I first get the Wii just making different Mii's.
Here's an online flash thing where you can test it out: http://www.joystiq.com/media/2006/10/mii.swf.