Well, we cheat in the module
When you edit a note in single view, we use the JForm class and there the notes field is set to an editor. In the module we create the form ourselves and we just go for a textarea field. You can have an editor there, but you'll need to hack the modules/mod_cnotes/tmpl/default.php file
The reason I didn't want to have an editor in the notes module is simplicity. If we were to go for an editor field, then you know how the joomla editor is - it would show 200 options and I would have to go and explain every user out there how to remove them.
I'll see what I can do on this.
Regards,
Daniel