I was in Germany for the Gamer's Summit and got to play some online MKDS (though I didn't get to keep my copy... lucky bastards ). It is teh awesome. Bad news is there's no online battle mode or chat. Also, I could only choose 20 tracks -- but a NoE rep assured me this was because the remaining tracks hadn't been unlocked (they will all be playable, according to him).
Oh, and Hideki Konno himself (who was in Canada) kicked my ass three times, but I actually beat him once!
At E3, I was sceptical wrt Nintendo's claim that 90% of users would try playting online at least once, but now, I actually believe this is possible. It's just that easy and accessable, esp. since Nintendo is setting up hotspots at gamestores and the like. So even if you refuse to buy the dongle, you can just go there, turn on your DS and race!