Amazon's Unknown Unknowns - NYTimes.com

Concluding paragraphs of a timely cloud reality check

"To be sure, such breakdowns happen all the time with old-style corporate servers. While they don’t have the dramatic effect of an A.W.S. failure, they may collectively represent much more downtime.
In a study commissioned by Amazon, IDC said downtime on A.W.S. was 72 percent less per year than on conventional corporate servers. While the financing of the study makes its conclusions somewhat questionable, its results are in line with similar studies about online e-mail systems compared with in-house products."

Amazon's Unknown Unknowns - NYTimes.com