Lukas Biewald of Facestat says Amazon S3, which is business-critical, is his #1 cause of failure:

Using Amazon’s S3 has about the same cost and complexity as hosting the images ourselves, but we had thought that the reliability of Amazon would be significantly higher. But that now seems wrong….It’s astonishing that serving content off our own boxes can be more reliable than serving content off of Amazon.

He’s also discovered that the SLA is not worth much – the business cost of the recent 7 hour downtime is far in excess of the 25% fee rebate.

S3 is cheap. Personally I think it is unrealistic to make S3 your storage service, have no plan B, and expect high reliability.

Amazon has a case to answer too. Salesforce.com has now just about lived down its 2005 outages; but incidents like these are terrible publicity for any cloud provider.