Ok, before I say anything else, I wasn't there to hear this. I heard it secondhand through two friends who were at Nintendo World today (Friday, April 28th).
Apparently, a kid asked Reggie about how the controller will be used to play Mario Kart, specifically how drifting will work.
The response from Reggie was that (the way my friend described it) you'll be able to dock the controller into a separate unit, and from there, tilting will work for drifting. My friend went on to speculate that this MAY be similar to the docking-bay controller mockup done by IGN awhile ago (back when the controller was first shown).
I have no way for you to verify this information other than word of mouth, so I understand if everyone would like to take it with a grain of salt. Still, my sources did hear this from Reggie himself.
Other tidbits:
No news yet about DS Lite pricing or release date.
No news on Mother 3 coming to America.
And of course, the standard "You'll know everything at E3" response we've all become accustomed to.