To answer your question, people do use various tools to extract Class Hierarchies, Call Graphs, Cross-Reference listing etc. The other HN thread that you have linked to contains some details. Lots of people do use them. You can easily add Doxygen/CFlow etc. to your make files to generate the diagrams during every build. The key thing for usage is that do not try to comprehend the entire system as a whole (all but impossible for large systems) but localize your study to a module at a time. Once you have the different pieces mapped out, you can combine them by hand.