I have for years been intrigued with Mind-mapping and Concept-mapping software offerings and the practicality of their use. I have yet to encorporate them in my work. There are great Mac apps out there, Nova Mind, Curio, etc.
I have been interested in a new blogger, Seth, who has been blogging some thinking about the subject, including reviews of solutions on the Mac. I'd recommend you have a look at Tech Landscape, if you are interested in this topic.