12:51 AM PDT We are investigating increased error rates for the EC2 APIs and launch failures for new EC2 instances in the US-EAST-1 Region.
Probably just fallout from the fact that EBS snapshots are stored in S3. If you can't create an EBS volume, you won't be able to launch an EC2 instance from it.
It appears that s3 based AMIs totally fail to launch as unavailable as well.