I use them a lot, both for work and personal stuff. For work I use them for course and lesson design (I'm a business trainer and a english language teacher) sketching out ideas and business strategies (I do a little business model consulting on the side too). They are also quite good for project management, especially if you use mind mapping software that auto numbers branches, makes it easy to create work breakdown structures. And of course, they're great for capturing brainstorming sessions, and I use them for note taking during meetings.
I like the iOS iThoughts, lots of great options for importing and exporting - I do a fair bit of presentation and document design starting with a mind map, then export it to Word or PowerPoint. Plus ithoughts has auto numbering, (the developer kind of added it at my request, a really nice guy, and actively developing the software) I also send it to xmind on my laptop where I can link ideas to actual files (excel, PDF etc.) I used to use xMind a lot, but I prefer mind-mapping on the iPad, it feels a lot more like working pen and paper.