I just wanted to say...
We should not be coding dialogs any more.
Instead we need to keep in mind breaking things down and making them reusable. One thing would be to avoid subclassing Gtk::Dialog. Instead we should have things more generic, and come up with a generic class based on Gtk::Container. These composit widgets could then be wrapped in a Gtk::Dialog for convenience, but then they could also be dropped into tabbed pages of a notebook, set vertically in a single window, etc.
And then in our code, we should try to avoid the physical concept of "pop up the style dialog", and instead replace it with the logical concept of "present the style chooser to the user". That's a very subtle difference, but can help in lots of areas.
Also... are there any other components we should come up with? Right of hand I can think of one in the 'Icon Preview' dialog I'm working on. It probably needs an document chooser, much like on the GIMP's layer dialog. However, others might need this too, so I was thinking it would be nice to have it generic and as reusable as the 'current color widget'. Anything else?