User notes are kind of like the original version of Visitor Messages. They were a way for members to leave publicly viewable messages on the profiles of other members before the blog and visitor message features were added. They (user notes) may not be around for much longer though as they are pretty much the same thing as visitor messages.
When you log into 420 Magazine, are you checking the box next to the login area to keep yourself logged in? It might be that you have been logged out prior to accessing this functionality.