There is a new Auto-Update for the Microsoft Xbox 360 Console available now, which does not add anything new feature wise according to Major Nelson:
Major Nelson: There is a mandatory global system update now available for Xbox 360 owners. You’ll get prompted for the update the next time you sign into Xbox Live. No new features or functions this time around.
Official Microsoft Xbox Site: The March 2006 Xbox 360™ update will prepare your Xbox 360 console for future system and title updates. This free update is available to all Xbox Live® members. Your console will be updated the next time you sign in to Xbox Live.