Grails is the Groovy equivalent of Ruby on Rails and I've been working with Grails for the past couple of months.
I'm a big fan of programming by convention and adopted Apache Maven many moons ago for just this reason. Grails also promotes programming by convention and by and large its quite reasonable for building server hosted web applications.
However one thing in particular has been bothering me. It seems that there is a view that Grails saves you the trouble of worrying about what goes on underneath it. This attitude is similar to one where using ORMs such as Hibernate save you the need to understand databases.
These attitudes are fraught with dangers as has been beautifully pointed out by Joel Spolsky in his Leaky Abstractions article.
I would agree that Grails can assist in increasing productivity but not at the expense of knowing what goes on under the hood. As Joel puts it, "... the abstractions save us time working, but they don't save us time learning".
Today I came across a Grails situation where I compared a newly instantiated domain object with one obtained through GORM. From my perspective both objects were equivalent as they had the same identifiers. I had wrongly assumed though that GORM had adopted the Hibernate convention of providing hashCode() and equals() on a natural key. Because Grails does all this magic for me, I had just assumed that this would be done. Well, it doesn't; and that's fair enough; how would GORM know what the natural key is? (declaring the natural key could be a nice feature for GORM). The point is that I could quickly find the problem because I'm familiar with Java/JPA/Hibernate and know that hashCode() and equals() should be provided for natural keys.
My advice is to stay curious. Don't be content with copy and pasting a bit of code you found using Google, seeing it work but not understanding it. This situation will bite you on the bum when your product goes live and you get a problem that you can't diagnose because you don't really understand what the code is doing.
Programming computers is a complex business and that's a fact that should not be avoided. Embrace the complexity.