Yep, loads of information has just come out about mario kart wii from nintencast.com.
Here's the low-down on the news:

- D.K’s snowboard Cross is a half pipe sort of track. You’ll be able to drive up the side of them and pull off awesome tricks in the air.

- Miis will be spectators in the background.

- Luigi’s circuit is still a simple track.

- Koopa Troopa will be a playable character.

- Coconuts Mall has players driving around a huge mall with multiple routes.

- D.K has a new go-kart.

- Names hover over players during online play.

- Motor bikes will be able to be used online.

I can't wait for the game you can see some new screens and the whole article on nitencast here: http://nintencast.com/news.php?subaction=showfull&id=1203337283&archive=&start_from=&ucat=2&