Today we are giving you additional insight into the operation of your Elastic Load Balancers with the addition of an access log feature. After you enable and configure this feature for an Elastic Load Balancer, log files will be delivered to the Amazon S3 bucket of your choice. The log files contain information about each HTTP and TCP request processed by the load balancer.
via Amazon Web Services Blog: Access Logs for Elastic Load Balancers.
This has been a long time coming but it is a welcome development. I’m looking forward to plowing through those access logs and running my own analysis on them.