The global shorcuts keys are a very useful way to perform actions which should works independently of the running application.
At this moment kde lacks the possibility to define new global shorcuts, like for example the volume control. In many situations the volume controls are not very fast (click over the kmix icon, click over the volume slider and pull it down until the volume is ok, click away to make the slider disappear).
I wish to assign the keypad +/- keys the volume control. An OSD bar should inform about the volume status.
That's what actually happens with gnome).