Alex, have you been using this? I'm always looking for better tools for laying my thoughts out, but I have yet to find one that feels natural enough to beat a big sheet of paper and a pencil.
Yes, I'm currently working on two separate books in this application and a bunch of other things. I've found that it actually lets you have more complex ideas than you would be able to have by starting with an outline (or god forbid just freewriting). The idea is that writing should be about ideas, and words are only there to express your ideas. Because of this it doesn't make sense to start putting pen to paper until you figure out what you believe. And it's a lot easier to figure out what you believe what you can drag and drop pure ideas around instead of mucking around with text.
Concept maps are another tool that lets you do this, but since writing is fundamentally either flat or hierarchical in terms of how you express ideas, I think mindmaps work better. (Concept maps are essentially like thinking in 3D, which becomes a problem when you need to translate your 3D ideas into 2D writing. Also, a lot of concept maps end up with really murky causality, which kind of defeats the whole point which is to clean up your thinking.)
