I've use both single and dual-pivot Shimano 600-series brakes and the dp's are my clear favorite. The argument that "sp brakes have enough power to lock the wheels of any bike so how much more power do you need?" is absolutely true but misleading.

I'm not interested in locking the wheels but in how much lever pressure you have to maintain while decending a long, steep winding down hill where you are going to be on the brakes for several minutes at a time. Ever come down from a seven mile long Rocky Mountain pass or a twisting off-camber downhill in West Virginia? Here is where the reduced lever pressure needed by dp brakes really shines.