For those who are using Ubuntu Jaunty, you will notice that there is a change in the way the system notifies you to upgrade software. In the past, an icon will appear on the system tray whenever there is new update available. In Ubuntu Jaunty, instead of showing the icon, the update manager will now pop up the window as and when it detects new update. While this is a good way to grab the user attention and get them to upgrade to the latest software version promptly, it can be pretty annoying for many, especially when you are in the midst of your work. To make it worst, if you close it without updating, it will keep on popping up in regular interval until you have upgraded your system.
Luckily, you can turn off this pop up feature easily and switch back to the old icon-appear-at-system-tray mode.
Open up a terminal, type
This will load up the gconf editor window
Navigate to Apps→Update Notifier. On the right, unchecked the auto_launch box. Close the window.
gconftool -s --type bool /apps/update-notifier/auto_launch false
gconftool -s --type bool /apps/update-notifier/auto_launch true