When putting together user interfaces with Interface Builder, you connect things together with bindings, actions and outlets and it's good. Understanding the result later on is a completely different matter. It can be time consuming and difficult to browse the objects inside one by one, trying to comprehend the whole. Even more so if you're trying to read someone else's work.
Out of that frustration came xibgraph. It takes a XIB file and outputs the connections contained inside:
At the moment it supports bindings and actions. Outlets are next.
It hasn't been tested on a particularly wide variety of XIBs, so it's very plausible it will produce wonky results or just outright refuse to work with your files. If so, patches and bug reports are welcome.
xibgraph is MIT licensed and written in Python. It requires PyObjC (it seemed like the easiest way to get XPath support on OS X) and probably Python 2.6. Everything but the DOT support should work without additional requirements on OS X 10.6.