Amazon Web Services continues to be a preferred destination for many people moving apps to the cloud. Security and related concerns continue to be important for enterprise-grade applications, and the AWS team has released more content helping users understand security models on AWS.
Overview of Security Processes: http://d36cz9buwru1tt.cloudfront.net/pdf/AWS_Security_Whitepaper.pdf
Risk and Compliance: http://d36cz9buwru1tt.cloudfront.net/pdf/aws-risk-and-compliance-whitepaper.pdf
(Not sure I'm loving these URLs, but... you can always find the latest here: http://aws.amazon.com/security)