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.
It is true that, like any developer Iike to learn things everyday, this is why I have done some development with PHP, with Ruby On Rails, and obviously with Groovy, Javascript and many other dynamic languages.
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.