I think it would be brilliant if you provide an option for users to create mind-map based notes.
You could start with simple features such as shapes, connectors and colors and then gradually provide more sophisticated features such as mind-map templates, images, icons, re-positioning of shapes etc.
I'd be thrilled if this feature is incorporated. I am a big fan of mind-maps and think they are great for note-taking in situations wherein you can't type a lot and for idea-generation.
Please please please do consider this.
Evernote for life!