I've found the following problems in IntelliJ GUIDesigner (versions 6 & 7, sorted by severity):
1. When renaming package containing forms with nested forms or images, the paths to nested forms and images are not updated (both in the sub-packages of renamed package and in external forms(i.e. sitting out of renamed package) referencing the forms inside the renamed package). The images paths can be fixed manually in GUIDesigner; nested forms paths should be fixed by editing xml (because instead of rendering the main form with some default panels replacing invalid sub-forms, the main form is not rendered at all and there is no GUI to fix the invalid references). (IDEA-16656 bug)
2. Cut and paste of non-empty panel is tricky - before pasting the compatible grid should be created manually in receiving panel. (IDEA-16660)
3. If GUI component's label contains HTML tags, the automatically generated field name contains the tags(without<>) too. (IDEA-16657)
4. When removing GUI component having attached listener from GUI form, neither its bound field nor listener are removed. I understand, that you don't want to remove code, but the result is the NullPointerException in a runtime. It would be nice to have a warning about orphaned fields. (IDEA-16659)
The first one from these problems is a real showstopper for the large project; all the rest are usability problems, causing frustration.
Please try to fix these problems (or at least first 2 of them) in the near future.