Elastic Beanstalk minimizes one of the objections I have about AWS - its lack of a simple deployment capability. This, as other commentators have spelled out, brings AWS even closer to being able to offer a pure PAAS in its portfolio, and bridges a gap with Google's AppEngine.
More information here: http://www.allthingsdistributed.com/2011/01/aws_elastic_beanstalk.html
and here: http://aws.typepad.com/aws/2011/01/introducing-elastic-beanstalk.html
I believe that PAAS solutions that support Java will offer the best early path for enterprises to bring their apps to the cloud. Elastic Beanstalk is starting with a Java container but promises more. I'd like to see a Python/Django environment - Django might well be able to evolve into a cross-cloud platform approach and help address the 'lock-in" issue.