I've just written a complete tutorial on writing plugins now as well, which you'll find here:
http://wiki.maemo.org/Mbarcode_Plugin_Tutorial
@joshn53: While working on the tutorial, I realized that there were a few more issues with using MaemoBarcodeWindow as the pointer in initInterface. It made it impossible to write a plugin without including QtDbus, which is not needed at all by most plugins. I've followed your advice and changed it to a QWidget* instead. Thanks for pointing out that possibility!