Tool support for dynamic languages may never be quite as good as that for static languages, but it is coming along. IntelliJ IDEA, NetBeans, and SpringSource Tool Suite (Eclipse) all provide some automated refactoring for Groovy code. I believe IDEA still has the lead in this area but the others are catching up.
I've found that with Groovy code, and especially with Grails, I don't need to do as much refactoring as with Java code. And when I do, it's easier to see what's what and what needs to change. There's a lot less noise in my code. I personally, rarely use an
IDE and I'm getting much more done in less time than I did using Eclipse or IntelliJ IDEA on JSF/EJB projects!
Just my $0.02
Dave