The Mii caricatures are a neatly executed idea. However, I personally wouldn't like to see the Miis into teen rated games. Mii presence would be too cute for that.

Smackdown vs Raw 2008 = example of Mii's in a teen rated game.. some what.

I think they're taking this Mii thing a bit too seriously. It was fun for a while, making charicatures, but it boils down to a poor man's character creator. Nothing more, nothing less.

Mii's could be a great oppurtunity for third party developers to push their games to extra sales. I don't feel Mii's and Mario should be in the same licensing category, but I suppose if Nintendo licensed Mario out to Sega for an average mashup of mascots, then the standard must not be too high to acquire it. 

Y'know, I still remember the original mention of the whole Mii concept. Originally the idea was to use that Gameboy camera or something like it in order to take a picture of your face and map it onto the Mii.