I use wxFB in such manner, that I design the main frame of the app while designing other panels, components of the frame, separately.
This combines advantages of both wxFB approach and "manual" approach - I can design stuff easily using wxFB without loosing ability to decide about composition of a frame during run time and possibly being able to reuse a panel with controls in more frames.
However, when putting panels into a frame, a problem emerges. The problem is that wxFB throws away sizers that I use when designing the layout, so it is very difficult to access them in order to insert a panel to the right place.
I would like to choose whether I would like a sizer to become a class' member or not (default being not ATM).
And although I have a feeling that C++ already supports this behavior, please add Python support for this, too (to my knowledge, Python has only public properties, so it is somewhat simpler)