I like this. I may try it out in spite of having too many note-taking strategies already (and this wouldn't replace everything else). Please do share your story - it's good marketing and it makes people feel better about paying (a measly) $5 when they understand what and who is behind it. Given the value and the ongoing work you'll be doing to add support for different contexts, I think you could raise the price to $10.

Are you using the extended attributes to store notes in each file? If so, that'd make it easier to pass the notes along to other people. I could easily see this being useful across art departments.

You probably have this on your to-do list, but you could use the new capability to badge icons in the Finder so I know there's a ghostnote attached.