MindNode looks interesting, but personally I don't like adding another propitiatory format that I cannot grok. In the past I had to export all my Evernote notes to plaintext because they increased their price. That's not a pleasant experience.

*.org files are just plaintext files with minimal structure. In the blog post, I attached a screenshot of opening a org mode file in TextEdit. It is pretty legible even when you open it with Notepad on Windows.