Disadvantage is that it is not so high-level, it is pure gtk so you need to write a lot of code just like in C, glade can help a bit I guess. Zenity is easier for simple dialogs.

I think it was straight recompile in scratchbox at that time, no porting needed, libffcall source was taken from debian I guess. Porting would be hildonization and perhaps also adding calls to osso etc. Possible but needs work. I mentioned it just for reference since it is related to zenity. I was thinking about using it to add gui to kernel and initfs flasher but never got to realization phase :-)