Since each note is unique to a user, why can't there be a column in your Joomla backend component where the notes are listed to have a user_id column so you know which notes belong to who?
Although it does sound snoopy, it's just a good way to keep track of the notes. I'm assuming it's possible since there is a field in phpmyAdmin. :-)
Also read the thread above mine. We both have conflicting ideas but we also both state good points. :-)