Awesome - in the past I have had to write my own code/scripts to manage attaching and EBS file volume to a new EC2 instance. This new feature will make it a lot easier to manage your own EC2 based services. If you would prefer a PDF with the complete documentation, then use this link.
This new feature will make using EC2 even easier for some applications - a welcome change.
That said, I have my own scheme for automatically mounting EBS volumes, assigning ElasticIP addresses, etc. and for some deployments I will continue to use temporary boot volumes and pull AMIs from S3.