1up just mentioned on their ListenUP Podcast that you can use Wii Balance Board as a control scheme (even though it's been mentioned/broken before, elsewhere). 

But the big news is they accidentally said that Piston Honda is returning! :D 

Check-it-out from about 1:22:30: http://podcast.the1upnetwork.com/flat/1UPYours/LUP042409.mp3

WOOT!  PISTON HONDA!!!

I thought they'd already said that all of the original punch out characters were returning (apart from Mike Tyson, obviously)? Or was that just something that I assumed?

GoNintendo just put-up a pic of Piston Honda and also confirms Great Tiger! 

Check-it-out!!: http://gonintendo.com/?p=81228 

More character confirming pics, anyone? 

I don't think the balance board stuff was really embargoed, I though Nintendo was pretty upfront about that.

The hilarious thing about the Piston Honda stuff is that not only did they mention it, but it was mentioned A) on multiple shows and B) acknowledged on the show they were breaking embargo only to keep talking about it and keep it in the show.

Granted, this is a Nintendo embargo; they tried to keep it hidden that Sonic was in Smash Brothers even after he appeared in a trailer.