The early indication of Windows Azure Storage downtime traced to an expired SSL certification; this forum thread is more of a “premortem” waiting for details from Microsoft.
http://social.msdn.microsoft.com/Forums/en-US/windowsazuredata/thread/751c85c5-b3b5-43ba-9d5b-770472ad79e1
I think many of us have learned about SSL expiration the hard way.
This is one of a general class of things people are bad at. As @Adrian_Colley pointed out, something should be done frequently, once or never. Anything else is simply leaving it to chance.