Apple's iMessage service, their iOS and OS X SMS- and MMS- like service, is currently down for a lot of users. It's been going down fairly regularly as of late, though not for lengthy periods of time. Game Center, Apple's online gaming service, has also gone down or suffered from poor service over the last week.
Everything goes down. Google goes down. Amazon does down. RIM goes down. Microsoft goes down. We go down. But reliability is a feature and if something goes down or suffers from poor services too often, or even if perception starts to give people that impression, it's a problem.