There's a standard trick I use to force myself into learning new stuff: I agree to write an article or give a talk on a topic that I want to know more about. Groovy - and dynamic languages in general - is one of those topics. That's why I accepted an invitation to talk about the differences between scripting languages next December and that's why I added "Using Groovy for testing Java applications" to the table of contents of a power workshop I submitted for this year's JAX conference which took place last month without me.
Here is where I got most of my Groovy knowledge: Groovy in Action by Dierk König et al. I got involved quite early as a secondary reviewer, so I had the PDF around a couple of months before final publishing. I made use of it - mainly as my source for quick (and offline) reference.
Two weeks ago I received the printed copy... And now I'm all fallen for reading a programming book cover to cover; a very rare thing nowadays after 25 years of mostly suffering from the bad state and style of computer "literature". Yes, I was given a complimentary copy, and yes, it's a great book all the same. It comes with more wisdom about language design and good OO than most books having "language design" and "good OO" in their titles. Put your favourite criminal story away, pick up GinA!