Eclipse is a really great editor, which I prefer to use, but the GUI design tools for Eclipse are lacking. On the other hand, NetBeans works really well for GUI design.
A few gotchas:
Another tip is that you can create Java Beans using Eclipse and drag-and-drop them into the Matisse editor. This allows you to create a custom GUI component or a non-GUI component (models, listeners, etc) and add it to a Matisse form. With listeners and models, you can specify a component to use an instance of your custom listener/model instead of the default behavior. You can also drag-and-drop in custom GUI components and manipulate them like any other GUI widget.