Some interesting possibilities...

Would the following be possible?

1) Headset connected/disconnected
(I know the NIT can sense this as the icon on the FM-radio player (N800) changes when you connect a headset)
a) When headset inserted, set volume to X
b) When headset removed set volume to Y

2) Application dependent
IF incoming VoiP call, stop all other audio, set audio to X and switch to Skype in full-screen.