After updating to Jaunty and now Karmic, I wanted to quickly jot down how to re-enable the old style update notifier....the one where it doesn't auto launch the Update Manager, but instead gives you just an icon notification. I found the documentation here:

http://maketecheasier.com/remove-the-annoying-update-manager-pop-up-in-ubuntu-jaunty/2009/06/18

Just open a terminal and type:

gconftool -s --type bool /apps/update-notifier/auto_launch false

Or, if you prefer the GUI method, then launch gconf-editor and go to apps -> update-notifier and uncheck "auto_launch".