Some desktop environments have their own hotkey launcher
utilitity. This nice, but it has a serious problem: if you
change the environment, you have to reconfigure all the hotkeys
(disgusting!). It's better to have a utility that do this task
separately.
The purpose of Xhotkeys is to provide this simple and easy
configurable hotkey launcher for the X-Window System. It should
work on all desktops (Gnome, KDE, Xfce, ...), and you can still use
their own launchers. Xhotkeys has a graphical GTK configurator, although it's possible to manage the configuration file manually.
The source code and binary packages for Debian (so, works also for Ubuntu) are available.