Xbox Live will be offline for a little while this morning, according to Microsoft's Major Nelson.
The downtime will begin at 2am PST (so 10am GMT in the old money) and will last for "up to 45 minutes". During this time, Xbox Live and the My Xbox bit of Xbox.com will be unavailable. Plus the Xbox forums will be read-only.
"The service maintenace is in preparation for the New Xbox Experience which will be available this Wednesday," reported the Major. Check out the NXE gamepage for the full rundown on all it's got to offer.