Gave you a 5 because you're apparently not up against a lot of competition. Not a bad thing...
I suggest you ajaxify it. You should make use of tabs.
Tab 1... List of note titles in order of creation. Sortable by category... be cool. Clicking a note title open that note in the same tab (or dynamically create a new closable tab!)
Tab 2.... create notes and categories.
Tab 3.... Default Note Settings... not fun having to click private each note.
Tip... display notes in html... at least as an option. Be nice to save links with notes and be able to click them. Be super cool to be able to enable a wysiwyg editor.
Thanks for at least a notes option :)... Good luck.