I have a tendency to post intentionally inflammatory posts that usually end up evenly divided between "yea" and "nay". But this time, I've got Rich Manalang's post from the JRuby on Rails front lines to back me up.
Rich is one of the primaries (Rich: THE primary?) behind Oracle's new Mix site, the first highly-visible public site based on JRuby on Rails. And after the experience he's convinced that JRuby is "the best way" to deploy Rails.
Read the whole article, but I think Rich's final paragraph sums it up pretty well:
This was an amazing project to be a part of. And one thing I’ll say is that for anyone working in a Java EE environment where you have to use the stack that’s there, the future is bright and it’s all because of jRuby, Rails, and the speed and agility at which you can build applications on that framework. I’m convinced that jRuby is [the] best way to deploy a Rails app if you need performance and flexibility. My prediction: next year will be the year for jRuby’s rise into the mainstream.