I have used a couple. One on the iPad and one on my Mac. For me they took a little bit of getting used to. Now I pretty much use them all the time. If it is a kick off meeting or the start of a new project that is what I use them for. If it is just a regular meeting I use a note taking application.
I also use MM programs when I am starting a project on my own. They can be very useful IMHO.
Curio and Mindmeister are the two I have used. Mainly Curio on the Mac though.
I have tried several mind mapping apps on the iPad, particularly for lecturing purposes. Most of them were deficient in too many categories to be of much practical use. However, I did find one that is very good--iThoughtsHD.
Really, the only things that are missing (for me) in iThoughtsHD are:
- children with multiple parents (this would be very powerful feature not found in any other app [as far as I am aware])
- enhanced customizability and flexibility with relationships between topics
- a Mac app version
I believe the author is working on the second, and I suggested adding the first. He seemed amenable to the idea. I do not know if there is a Mac version in the works.
You might also want to checkout iDesk. It is a pretty good diagramming app. I use that in the classroom to good effect as well.