In case anyone's interested, I've started a simple HOWTO blog post for 
serving up JRuby + {Rails,Merb,etc} if you already have an Apache server 
(which I suspect is a typical setup for most folks serving Rails and 
friends):

http://blog.headius.com/2009/04/apache-jruby-rails-glassfish-easy.html

I'm no Apache expert, so I'd really love suggestions, but basically it's 
as simple as running the app in JRuby (using GlassFish gem or Mongrel or 
whatever) and setting up Apache to proxy to it. JRuby side will handle 
all requests thrown at it.

- Charlie