Kubuntu 9.10 Karmic Koala has a nice notification system called Ayatana. The notification system of KDE is ugly in my opinion, so I like Ayatana very. It is very beautiful, and it is more beautiful if the desktop effects are enabled. Ayatana is a Canonical-community joint effort to discuss and promote improvements to the Ubuntu user interface. See this link for more information.
However Ayatana is not part of Kubuntu 10.04 Lucid Lynx, because it was a patch for KDE. If you liked Ayatana, and use Lucid Lynx, then take a look at the Colibri. It can be installed from the repositories, and has the same functionality like Ayatana. Currently only the position of the notifications can be changed, and not all notifications will use Colibri, for example the file transfers. Before you start using Colibri, some preparations must be made: uncheck the “Application notifications” in the System Trey Settings dialog box. After then check that the
contains the Exec=/usr/bin/colibri line. At last you have to configure KDE to start Colibri at login time via System Settings → Advanced → Autostart module, just add /usr/bin/colibri and you are ready. Here is a picture about Colibri (click on it for bigger size):