I've often used mind mapping when needing to brainstorm ideas, relevant concepts, and organize them into their hierarchical levels of depth.
I also plan on writing a book, which will start as a mind map - the central focus/topic in the middle, 7-10 questions as the next level, 2-3 answers for each topic, and a few other branches in between as needed for additional info, definitions (if needed), background, etc.
I could see it as a useful tool in preparing lesson plans, and for students to help understand topics. Students could also use them in preparing presentations or reports, including essays, and even studying concepts for tests.
The map above was created with Inspiration 9 on the Mac, and was very quick to produce. I definitely can recommend this software tool as a useful tool. I think that a hand map could sometimes be quicker or more effective to a point - but when the map gets large, the paper and pen fail. It is also more difficult to digitize a large mind map and have it look good/legible. I don't often recommend commercial non-free tools, but this one seems to be quite powerful and useful, with fantastic export options to MS Word, OOo Writer, Apple Pages, Web/HTML, PDF, GIF, JPG, PNG.