updated 03:40 pm EDT, Mon September 17, 2012
Problems not omnipresent amongst users
Some users of Apple's iMessage service are having problems with delayed messages, or even messages failed to be delivered at all, according to complaints. In some circumstances people are getting read receipt notification errors. The issue in fact appears to be inconsistent as a rule, affecting some people but not others, and even those with trouble are occasionally getting a reprieve.
iMessage is integrated into the latest releases of iOS and OS X, and for the former serves as a kind of free, platform-exclusive SMS service. The current outage echoes a similar difficulty with iCloud Mail, which lasted for over two days. Apple will likely want iMessage fixed by Wednesday, when it's planning to release iOS 6.