Grails IA didn't come out very long ago (Sept? Aug?) and from what I've read, it's pretty much as up to date as it gets.
This book (Quick Start Guide) seems like a great "This is Grails, let's do something with it quickly" guide. Just like the title says, I guess.
I haven't read it (did just win a copy at a local event) but will definitely be taking a look as even though I've done some of the Grails IA examples and other Grails coding on my own, there are lots of 'apps' that I think up that could be done quickly and I'd very much like to read Dave's guide on how to do that.