Get started with Ruby on Rails using JRuby and App Engine
rails-primer.appspot.com
rails-primer.appspot.com
I'd be great to see some info on how to run migrations and other rake tasks on app engine.
From the benchmarks I've seen of Python / PHP / Ruby, etc. Ruby isn't blisteringly fast anyway, and if run in an interpreted Java VM in a relatively new in-house Java runtime then it might not be a great solution for web apps that need speed or scalability.
Not bashing Ruby here, nor the app engine. I guess it'd be a neat environment to write small / demo apps in without shelling out for hosting.