updated 10:15 pm EST, Mon December 17, 2012
Though problem was modest, may have affected wide range of users
Though Apple's new System Status page for iCloud provides users with at-a-glance notification of problems (and offers a timeline showing exactly how long any service interruption occurred), a brief outage on Monday -- that affected all of the iCloud services apart from iTunes in the Cloud and iTunes Match -- shows that the revamped page does not always specify what percentage of users are affected in a given incident. Apple's report on todays incident, which lasted just over an hour, simply says that "some" users were affected.
The iCloud service has seen periodic interruptions that affect at least some portion of users on a more-or-less monthly basis since it changed over from the previous MobileMe incarnation. On the whole the system has been seen as more reliable than previously, and actually compares favourably to its nearest rival for email services, GMail (Google and Gmail have also struggled with some recent outages as well).
Nevertheless, any outage is bound to inconvenience some users, and the most recent iCloud one lasted for over an hour compared to GMail's more frequent but usually very short incidents. In particular, users in need of a service such as Find My iPhone (which also works with Macs and other iOS devices) would be very inconvenienced by a prolonged outage.
According to Apple, the outage lasted from 2:35pm to 3:49pm (presumably PST since Apple is based in Cupertino, though the site doesn't specify). The iTunes Store was down early Sunday morning, but only for 49 minutes in the wee hours when usage would have been light (only 2.3 percent of users were affected, in any event). The system status page offers a timeline of recent incidents, but only goes back about three days at present. Presently, all services are up and running.