"Why on earth would you want to create a Cocoa application without using Interface builder?"
That's the basic reaction you get if you try to seek out help online in writing a Cocoa application from scratch.
There may not be a lot of valid reasons but if there is at least one reasonable answer, then the question should be moot.
Our applications at DVFilm are cross-platform. The user interfaces are very simple. The majority of the code is written in C/C++ and in the business logic. So I have not given up on the idea that the simple form-based UI can be written in such a way that the majority can be shared between Windows and Mac.
There, that's my "reasonable" explanation on why I am crazy enough to consider creating a Cocoa application programmatically. If that doesn't satisfy, here is another reason.
I have inherited a Carbon application (a QT template app, actually) and simply want to add a single dialog using existing Cocoa code.
If neither answer satisfies, I DON'T CARE. I do appreciate all the arguments for stopping my Tilting at Windmills but THEY don't satisfy ME. If you can't bring yourself to suspend your disbelief and offer help, I'll figure it out on my own.