http://aws.amazon.com/message/65648/ Postmortem for the April-2011 EC2/EBS outage. It looks like a human errors plus unfortunate cascade of events lead to a requests storm that brought down EBS storage. Also, it appears that Amazon mis-estimated spare storage capacity needed for recovery from such events.
http://justinsb.posterous.com/aws-down-why-the-sky-is-falling A blog post explaining nature of the current Amazon AWS outage. The deal is that several so-called availability zones (AZ) failed simultaneously in amazon US-EAST region, even though amazon’s FAQ describe such event to be unlikely. Many interesting comments – read them!
http://blogs.skype.com/en/2010/12/cio_update.html?cm_mmc=PXBL%7C0700_B6-_-downtime-20101229 detailed notes about skype outage on DEC-23/24 2010