The Netbeans team has just released 6.5 beta. Having been testing the latest nightly builds, I think that you'll be pleased with the beta once you try it. The Groovy/Grails support is in great shape. New features have been added since M1, including a plugin manager and different application layout.
You'll also enjoy the automatic deploy on save feature. This really helps to speed up development time.
Congrats to the Netbeans team on delivering this beta of 6.5...it is looking so far.