Just thought i would put a response together for this post:
Grails dark side
In my opinion the Grails sweet spot is for developers who already have years of experience of building web app with spring/hibernate/sitemesh and java.
Basically it is the "iron man suit" for an already established "Tony Stark" developer. The iron man suit is at its most powerful when it is controlled by Tony Stark. A man who has years of experience of solving problems. The suit simply enhances him :)
I have years of experience of using the spring/hibernate/sitemesh/java stack along with deploying java web apps on java app servers. So Grails is my "Iron Man Suit"
For me Grails is essentially the same core deployed in the same way. The difference is that Grails + Groovy is literally super glue for these components. Almost like comparing assembling your own Ikea furniture vs carving your own out of wood. Except the end quality is even better.
So thinking that you can get the absolute most out of Grails without knowing anything about spring or hibernate etc is ignorant. And actually being ignorant of the underline technologies often leads to assumption that a bug with the underline technology (eg hibernate) is a bug with Grails.