According to Amazon the fail rate of EBS volumes is:

As an example, volumes that operate with 20 GB or less of modified data since their most recent Amazon EBS snapshot can expect an annual failure rate (AFR) of between 0.1% – 0.5%, where failure refers to a complete loss of the volume

http://aws.amazon.com/ebs/

However, I was curious to know the fail rate of EBS snapshots and private AMIs that a system admin would take. Since the EBS snapshots and AMIs are stored in Amazon s3, is it safe to assume that the likelihood you cannot rollback to a previous snapshot or AMI the same likelihood that a file gets lost in s3?

Amazon S3’s standard storage is: ... Designed to provide 99.999999999% durability and 99.99% availability of objects over a given year.

http://aws.amazon.com/s3/