I've been developing with jruby on GAE for about a year. http://code.google.com/p/appengine-jruby/ http://code.google.com/p/appengine-jruby/ There has been a g

I've been developing with jruby on GAE for about a year. http://code.google.com/p/appengine-jruby/ http://code.google.com/p/appengine-jruby/ There has been a good deal to learn, and some changes to adapt to along the way for the jruby library - which is to be expected. My sites are mostly noncommercial and don't get a ton of traffic, so their generous free/cheap plan was an incentive I couldn't pass up. Alternatively you can do very little for free on Heroku (the other 'free' hosting option for Ruby). It's been a good experience overall, but this last month I have spent weeks pulling my hair out trying to do a join. I have a work-a-round in place now, so hopefully it will be smooth sailing from here on. If I do run into performance issues I may have to switch, but then it won't be to hard to migrate and I've still had a free development environment which has pushed me to learn and cost me nothing.