On Monday, 9/29/2008 from 12:01 AM PST for up to 24 hours, Xbox Live will be offline for maintenance. As a result, Xbox LIVE and the ‘My Xbox’ section of Xbox.com will be unavailable, and the Xbox forums will be in read only mode (you won’t be able to post.) The remainder of Xbox.com will be available with limited interruptions.
This service maintenance is in preparation for the new Xbox experience which will be available later this fall.
Let me reiterate: When the service returns, you will not have any new features and you will not have the new Xbox experience update. That will happen later this Fall.