You mentioned a good point about JavaScript. By sticking with Java, it'll be easier for me to get started and yet I will still learn a ton on the client side with new things like JQuery.
However, I read that the Play framework might be better than Groovy on Grails[1]. Have you heard of it and, if so, what do you think about it?
[1] - http://stackoverflow.com/questions/1597086/any-experience-wi...
As for Play Framework... yep, I've heard of it, but I haven't used it. Everything I've heard has been favorable, but by the time I got wind of it, I'd put a lot of time into Grails and am using it pretty heavily now. And if I were to switch away to something else now, I'd look hard at Lift or something else using Scala. But Scala would probably have a steeper learning curve for you, which is why I didn't mention it before. With Groovy, the syntax is mostly a superset of Java, so it's very easy to start writing Groovy as just "java files renamed to .groovy" then introduce the Groovy stylings and idioms as you learn.
But anyway, yeah, spending some time playing (no pun intended) around with Play and evaluating it, probably wouldn't be a bad idea either. :-)