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Oh wait, the only downside to not implementing dconf is that you won't see your application installed by default on the Ubuntu live CD. So no, nobody must do anything.
Indeed. The library is already being written so an application which wishes to be part of the default installation only needs to add the library and to save/store its settings via that. Not really a big effort needed. And besides, not all apps are going to get on the default installation anyways.
I don't get all these comments saying "I have wanted Qt apps in Ubuntu for years, and now they are doing it. Those bastards!"
I suppose they were happier complaining than actually getting something. And still, Qt apps have been available in Ubuntu for years, the only difference now is that it's possible some Qt apps will be included by default.