I'm no expert UI designer, but my mind is better kept in code, not diagrams. When building iOS applications for the iPhone and iPad devices, Interface Builder is a great tool to get a bunch of stuff fleshed out quickly, but at least for myself, I get frustrated quickly when my project grows and I have to constantly switch between a half dozen windows trying to understand why one object isn't updating or displaying correctly. One line of code would fix it, but since the entire interface is in a Nib, I don't even know where to put that one line of code to keep my code clean.