When you first create a new Griffon project (File | New Project | Groovy | Griffon Application), you will be prompted to provide a path to your Griffon distro. Here's how I've set mine:
I discovered today that even though I haven't set 'GRIFFON_HOME' anywhere, Griffon works in NetBeans IDE, thanks to the above setting in the Options window. I.e., I downloaded Griffon from the Griffon site, unzipped it, didn't configure anything in my evironment, started up the IDE, set the above setting after having been prompted to do so, and was then able to create new Griffon applications.
My favorite feature of the Griffon plugin in NetBeans IDE is the fact that I'm able to simply open a Griffon application, i.e., without importing and without adding any kind of metadata in any shape or form. For example, go to the Favorites window (Ctrl-3), browse to your Griffon distro, right-click one of the samples, and notice that you can simply open the Griffon application into NetBeans IDE 6.9 Beta:
When you invoke the action shown above, NOTHING is added to your Griffon application, no small secret property files or whatever, of any kind, i.e., your sources are completely untouched. So you can view/edit/whatever the application in NetBeans IDE 6.9 Beta without fearing that anything weird is happening to make all that possible.
Undoubtedly there are still problems somewhere somehow, so Griffon enthusiasts are welcome to try out the plugin and provide feedback:
Older versions of the plugin are available (here on Kenai), but I will not support them anymore, i.e., I myself personally am not going to try to solve problems occurring in previous versions. All the sources are on Kenai, so anyone is free to access them and add features or whatever.