Stevey had a series of articles where he implemented Sokoban in a bunch of JVM languages, and Groovy did very poorly. I can't find a live version of the article, but here's archive.org's copy:

http://web.archive.org/web/20060720091555/www.cabochon.com/~...

Groovy just seems pointless to me. It's taken too long to get anywhere, and I can't think any reason to use it over JRuby, Rhino or Scala. JRuby and Rhino have the benefit of being implementations of popular languages, basically getting years of experience, tooling, docs and code for free. Scala adds novel ideas not found in other JVM languages, and makes certain types of problems much easier than they would otherwise be. Groovy is a less powerful version of Ruby with a Java like syntax. It's awfully hard to get excited about that.