In case you missed this when I posted it over in the Xbox forums this past weekend:
On Tuesday May 2nd from 0200-1600 PT Xbox Live, Xbox.com and the forums will be offline for maintenance.
During this time, Xbox.com, the forums and Xbox Live will not be accessible.
Click this link to find out what time the maintenance will begin in your time zone
You have the entire day to work on your offline games, or even venture outside into the daylight if you so desire.
Oh, and this is for maintenance only not a dashboard upgrade as many people think.