Last week I discussed dynamic languages with some consultants. This discussion was done in the context of integration of scripting technologies into Java EE environment. So the integration to the VM is important, I also think that the learning curve is a thing to consider.
The discussion moved quickly to an argument about which language is the best... Hard to say, but I would expect that to be more productive in enterprise it is better to use a "Java Like" syntax that allows you to leverage the power of scripts. Based on this comment it is for me a no brainer to say that Groovy is more interesting to a core Java developer than JRuby (or other Jython, Jacl, ...). I do not even want to go in the details about VM integration, performances and so on...
So in this context, A. Sundararajan has posted a very interesting comparison of Java, Groovy and JRuby syntaxes.