I'm honestly really thrilled with all the choices on the JVM; not just JRuby, but Java, Clojure, Groovy, Scala, Fan... and they all play together incredibly nic

I'm honestly really thrilled with all the choices on the JVM; not just JRuby, but Java, Clojure, Groovy, Scala, Fan... and they all play together incredibly nicely. It's an amazing productivity boost to be able to use a dynamic language (like Ruby or Groovy) to handle all the business logic and glue code, while at the same time being able to take advantage of the speed of pure Java when you need it.