Right, hugopl (in #pyside) pointed out that my widget variable is being decref'd as soon as the window is created, so simply making the widget a member of the class (e.g. adding it as self.widget in __init__() sorts that out and displays the window).

Looks like Python scripting is go!

I'll come up with an example code tomorrow, and also one which uses DBus to notify/start external apps (e.g. Map apps for geo:// payloads).