In xfce 4.3 svn, everything is becoming Fitt's law friendly.  Xfce4-mixer does a
great job of this for the launcher itself, but the volume bar does not.  If you
move your mouse up a couple pixels from the bottom edge, the volume bar
scrolling works.

Reproducible: Always
Steps to Reproduce:
1. Put the xfce4-mixer applet in the bottom right corner
2. Drag mouse to far bottom right corner
3. Use mouse scrollwheel to try to adjust volume

Actual Results:  
Nothing!

Expected Results:  
The volume should increase and decrease accordingly

I'm assuming if the volume bar were extended to the top and bottom of the
applet, it would work, though I'm not sure.