Okay. I've "completly" finished the game as of yesterday. And by that I ment that I've raced through all the modes. There's still some characters I haven't unlocked yet, but I assume that you have to go through time trials to get them or whatever. I hope you don't have to go to Wifi to do stuff because I don't have proper internet at home. But I doubt Nintendo would be that evil. I guess I'll just have to wait and see...
So far I've unlocked Birdo, Bowser Jr., and Baby Luigi. Nobody too interesting...