Interface Builder doesn't let you do anything very dynamic (moving panels, things that animate, etc) anyway. In my experience, a person experienced at programmatic view creation is a bit slower on initial creation, but a lot faster at refactoring or changes. A few well placed variables, for example, gives you a lot of instantaneous visual control.
This doesn't scale when doing projects where the UI tends to be redesigned every few days.
In a few hours it is possible to design UIs that some require days to do it.