I have done some JRuby + Sinatra coding for AppEngine in the last 6 months, but I keep running into problems that I simply don't have when I use Java. I worked through the linked article several days ago and hit errors (at least on my dev system) near the end. I started converting an app to JRuby + Sinatra several months ago, and things were mostly working, but I ran into enough problems to postpone the project. I can be patient.<p>That said, I expect the JRuby support to keep getting better, and I hope that soon I can mostly switch to JRuby.