This is the fruit of my spending over 2 weeks learning Chef. It produces an EC2 instance with the latest everything (Ruby 1.9.2-p290, Nginx 1.0.6, Mongodb 2.0.0) and does rolling restarts of the unicorn processes when new app code is deployed. The deploys are nearly seamless, similar to the experience on Heroku.
Here's an earlier post on a more basic Chef setup: http://reedlaw.smashingboxes.com/Rails/Chef/2011/09/19/setti...