Fit for use
I am a big fan of OmniGraffle and use it heavily for all kinds of design efforts. Yet, for a quick brainstorming session - I use SimpleMind. It works great on the iPhone/iPad - making it a reasonable replacement for a napkin to capture that spur of the moment brilliant idea. The OPML export means that the ideas are not locked in SimpleMind.
chuston about
SimpleMind Pro