While I understand that its not like Groovy requires a large change to start using (unless your running Grails I guess). I just started using it a month ago when I ran into a hunk of JSF controller code that would be drastically simplified with the use of closures. It only took 1 dependency in the pom and a tweak to the maven compiler plugin and I was off and running. It integrates so easily with Java that no code changes anywhere but the controller I was writing were needed.