If you don’t like the new notification center feature in Mac OS X 10.8, you can disable it (for all users on system level) with the following defaults write command.
sudo defaults write /System/Library/LaunchAgents/com.apple.notificationcenterui KeepAlive -bool false
You will need to provide your admin password.
After a reboot the notification center will be completely disabled. The current loaded instance of notification center can be killed with the command:
killall NotificationCenter
Re-enable the notification center with:
sudo defaults write /System/Library/LaunchAgents/com.apple.notificationcenterui KeepAlive -bool true