Tiago Fernandez in his blog reported some results about benchmarks using Java, JRuby, Groovy and Scala. I know: we can talk about benchmarks for days but in the Internet there are a lot of them and the performance problems of the scripting language is not a news.
Results show that Groovy is very slow in comparison to the pure Java and the Scala scripting language. This could be a serious reason to be worried when your application created with Grails or RoR goes in production...
So, why don't you use a real Java RAD tool like Roma Meta Framework? :-)
You can develop shortly without using a scripting language with the benefits of great refactoring support (Eclipse, Netbeans and IntelliJ are master on it) and performance and scalability!
The source: http://tiagofernandez.blogspot.com/2009/05/java-integration-with-groovy-jruby-and.html