I'm running KUbuntu 10.04.1 - I click on "System Settings" from the KMenu, click on the advanced tab, and start up "Service Manager". In the lower pane, I see "Free Space Notifier" is running.
Update: It might be a monitor for the free disk space in your home partition. Can anyone confirm this?
According to the package description, it monitors free disk space on the Home partition and warns you on low disk space.