Today I updated the NetBeans Griffon Plugin to NetBeans IDE 7.0.1. One change is that there's now a new module (i.e., the Griffon plugin now consists of 3 modules), which will let you create Matisse GUI forms in your Griffon application:
So, right-click the "Views" node, then choose New | MatissePanel.java and then you'll have a JPanel in the Matisse GUI Builder.
Some more info is here:
Get the NetBeans Griffon Plugin here:
Comments and feedback is very welcome, here or on the page above.