After a rough patch last week for iCloud, Apple has been having some issues today with iMessage. Reports on MacRumors and Twitter indicate some people were having trouble using Apple's SMS replacement. Problems included messages not sending and error messages.
It's not a problem for everyone using the service, but it had many Apple users gritting their teeth. Many people are now reporting the service is working again, but my personal experience with iMessage is that most of the time it works, but several times a week the service stumbles and my iPhone has to revert to standard SMS.
Apple needs to tighten up iMessage and the iCloud service if it wants to compete. Apple owners tend not to suffer in silence.