I'm now building a IT-test harness to check I don't break things anymore when changing code.
The last "oups, I broke the plugin" is related to running GWT-SDK tools on Mac. I don't have one myself so can't test on this platform.
If you want to support the gwt-maven-plugin, please lend me a Mac Book or Mac mini (low-cost Mac, if 600€ can be considered "low"). If your company want's to support the plugin I'd be pleased to add a sponsoring link on the plugin site.