Game Developers Conference. There are no other details provided, and trying to discern any surprise announcements based on that speech title is pretty much a fruitless endeavor.
Iwata last gave a GDC keynote in 2006, when he showed Brain Age and Legend of Zelda: Phantom Hourglass. Company man Miyamoto gave the 2007 speech and revealed ... the Everybody Votes Channel. As for last year, the House of Mario's presence was limited to a handful of sessions. Get your bingo cards ready, Iwata's keynote is set for Monday, March 25 at 9 a.m. PST (that's noon, Joystiq Standard Time).