For your projects, did you have a favorable experience with Groovy? How big was the project? Were there issues with the language? Did you consider Jython, JRuby or Clojure?
My team recently implemented a small AtomPub service using Grails (and by implication, Groovy). Overall, it was a nice experience. We briefly considered pure Java and JRuby as alternatives, but not Jython or Clojure. The team went with Groovy because it was somewhat more familiar-seeming than JRuby, but offered more flexibility than Java.
Here are some of the issues we encountered: