Much like x10 two weeks ago, this is Nintendo's media briefing for the first quarter of the year.
Don't really know what to expect, except I would guess more information on Mario Galaxy 2 and Metroid Other M.
We should see some new DSi/Wii-Ware games, and of course hands on with their q1/q2 releases such as Sin and Punishment 2, Monster Hunter Tri and Red Steel 2.
The event starts in just about an hour or so shall be updating, I guess this post.