We have the first movie of Mario Kart DS and it shows the kartsters whizzing around a ported version of Yoshi's Circuit from Gamecube's Mario Kart: Double Dash!!
The quality and speed of the game is bang on and everything you would have hoped for. However, the touch-screen isn't used to any great effect. You get a very predictable map and position roster. While this does clear up the playing screen by reducing necessary game furniture, we can't help but be disappointed that it doesn't enhance the game in any way.
At the very least, Nintendo could have thrown a reverse view in there so you could easily monitor those hot on your tail. Nintendo stated in their DS press conference that they've given developers the tools and it's down to them to use the touch-screen in an imaginative and innovative way. That's all very well but you'd think the most innovative developer of them all - Nintendo - would have led the way on their own machine in one of their AAA titles.