Getting Your Ubuntu 8.10 Notification Back In 9.04
If you miss the notification that used to be in the 8.10 notification area telling you new updates are available you can get it back by quite easily by issuing the following command.
gconftool -s --type bool /apps/update-notifier/auto_launch false
Then you just kill and restart update-notifier and you will have your icon for update-notifier back (to check it straight away, run: sudo apt-get update).
Note: This will also stop the update manager window from automatically popping up every time you run apt-get update which is reason enough to do it on its own.