My 2 year old won't stop talking about it ever since he saw a promo video at walmart.
He had seen Mario (and is adept at walking him off cliffs or jumping in place in NSMBU and SM3DW). But the idea of Mario driving blew his little mind. "Mario driving car" is all I've heard all week. After being told he has to wait until Friday, "No, I want Mario drive car NOW," sometimes followed by a mini tantrum. I could let him play MK Wii, but I don't want to spoil it!!
There's little to no chance he'll be able to competently control the game for awhile yet, but damned if he won't try.