Major Nelson has this morning advised that on Monday April 21st from 1000-2000pm GMT Xbox Live will be offline for maintenance. As a result, 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.

The downtime is for maintenance, there are no new features being added to the Xbox 360 console or Xbox.com when the service comes back online.