I am running ubuntu 9.10. Can you please tell me if there is a notification system in ubuntu 9.10? (like the screen cast below), and if yes, how can I enable it?
Yes, there are various notification daemons available for Ubuntu. Generally these comply with the Desktop Notification Specification, a freedesktop.org standard for doing notifications. They use D-Bus for communication.
The Linux kernel provides a notification feature known as Inotify, and Ubuntu provides various packages supporting that functionality. This supports file watchers, notifications on device states, etc.
Generally, the notification daemon is already enabled; to use it, you need to add applets to your Gnome Panel (the top bar). All the systray-like icons at the top right of the default Ubuntu screen are notifier plugins.
You can find additional applets in the Ubuntu package repositories, through your favorite package manager (eg Aptitude or Synaptic).
For more info see:
The notification system is enabled by default. You can send notifications to the notification daemon from the terminal like this:
Look in the man page for notify-send for more options.