Tried to do a little multi light setup tonight. From the setup shot you can see the 580EX fired into a 32" silver umbrella, a 430EX on the table bottom right, 'snooted' through two books (too lazy to get out the cereal box yet), and a silver reflector to the right of the subject (toy horse).
Finally, with teh 430EX snooted light fired at the back of the horse's head:
One thing I realized is that the umbrella really spills the light, as can be seen by the otherwise unlit background, which is really quite grey (not black).
This one I took later, with the reflector moved behind, and the 430EX fired at the reflector with a red gel: