I've recently been playing around with JRuby and found the switch from MRI to be hassle free. One of the advantages of JRuby is it's portability. You can use nearly all Ruby code straight away on the JVM without having to do any code changes, you just include the jruby jar in your classpath.
Another advantage is Java interoperability from JRuby (just require 'java'). I've found this useful when using JMX to check certain conditions are in place while performing releases and for general monitoring.
The following script uses JRuby's Java integration to walk a given ObjectName's attributes within JMX.
When invoked against a running JMX instance this will return something similar to:
Hopefully this is of use to you, or inspires you to investigate JRuby a bit further. I'd highly recommend it for Java shops who want to take advantage of Ruby's scripting ability.