This being a major keynote, and this being Nintendo, anything could happen. Nintendo could stick with current form and announce, well, nothing. Just a feel-good story about how much money they're making.
OR...they could do something special. Some are claiming that he'll be up on stage showing off a bunch of new games for Wii, DS and WiiWare, both first-party and third-party.
Now, he might do both! He might do neither. That's the thing with Nintendo. You never know. So tune in at 9. And bring enough tea and biscuits for an hour-long liveblog.