The first day after the vacation was fairly productive, after all. In preparation for an upcoming PNEHM article, I've successfully installed a snapshot of IDEA 7.0 and built a Subversion snapshot of the Groovy/Grails plugin. This is the first thing I tried out - it looks very promising:
Dynamic typing and completion!
Update: it turns out IDEA also completes the Groovy additions to the JDK. Not completely unexpected when you've seen the screenshot above, but nevertheless very nice!