The "Sessions" part of the following location of the notifier's integration with
the desktop is missing:
"Gnome: System Preferences -> Startup Programs -> Update Tool Desktop Notifier"
It should be:
"Gnome: System -> Preferences Sessions -> Startup Programs -> Update Tool
Believe it or not, on multiple occasions, I've relied on the online help to
remind me of both the location of the per user Update Tool preferences and how
the notifier is hooked into the user's desktop.