updated 04:00 pm EST, Mon November 28, 2011
Regions coming back online
(Updated with resumed service) The Mail component of iCloud has been suffering from an extended outage, Apple's system status page shows. "Users may be unable to access iCloud mail. Normal service will be restored ASAP," a message reads. The trouble has been ongoing, however, since at least 11:07 AM Pacific time.
Apple's support forums have been clogged with complaints about being unable to access any Mail functions. The service may already be working again in some regions though, such as eastern Australia or the northwestern US.
Update: Apple is officially claiming that all services are back online.