I've GUI-fied a "background" program I have, to make it easier to deal (read - double-click on it and hide it in the system tray). Additionally, since Ubuntu 8.04 sports lots of drag & drop and it's awesome, I've included it in my program too (drag and drop installation of addons to it. You'll see that it, basically, modifies the config file properly in the end).
My first GTK app, went with Glade 2 code generation for the GUI and never opened Glade again, tinkered with the sources manually and did the application logic.
Pic of what I was using before:
Video demonstrating minimizing & drag and drop: