The big problem with Interface Builder is that, most of the time, its layout view bears no resemblance to what your UI actually looks like within the app. Deciphering the meaning of overlapping grey boxes in IB is often just as difficult as reading code. "WYSIWYG" it ain't...
I'm working on a design tool that aims to fix this: http://neonto.com
Neonto Studio is a completely visual environment with support for vector drawing, video, smart guides, multi-device layout with full previews, and so on... There's no coding involved -- this is an app for designers.
The tool generates readable iOS and Android code, and there's no special runtime involved, so it's ridiculously easy to take a few screens designed in Neonto Studio and drop them into a larger app.
It's currently in alpha testing. I'm hoping to release a full beta in the next few months. If you're interested in trying out the alpha today, I'd love to have your help -- just drop me an email at pauli <at> neonto dot com!