Take this with a grain of salt, as I haven't tried Groovy/Grails, but in my experience several of the other rails knockoffs were the genuine Rolix's of the framework world.

Rails is not perfect, but ruby and leadership by innovators who think a little different made it what it is. Will you see that in me-too frameworks? Will they ever do more than copy ideas and stay a step behind?

Plus, the difference between a dynamic language and java is something like the difference between travelling at light-speed, vs. faster than light. In Java you travel (code) in a straight line. In Rails or a dynamic language, you can fold space-time so the destination point is only a few lines of code from where you are now. Cleverness gives you more leverage in a dynamic language. ROR is solid enough, and Jruby can run rails now.

Eric