Amazon experienced issues with network connectivity and increased API latencies. Both of the problems happened on September 16 2013.
There were connectivity issues between two Availability Zones affecting a small number of instances in the US-EAST-1 region betweeen 7:40 AM PDT and 9:49 AM PDT .
Later that day, between 1:12 PM and 3:21 PM PDT, Amazon experienced delays in returning DescribeInstances results for newly launched instances in VPCs in the US-EAST-1 region. During this time new instances in a VPC successfully launched but were not reported by DescribeInstances API calls. Also during this time some customers may have experienced increased latencies or error rates when calling the DescribeInstances API, including calls for instances that are not in a VPC.