Stirring the pot a little....
Am I the only one here that actually sees a difference a diffuser creates when shooting outdoors? Direct flash gives really harsh lines around the nose, eyes, cheekbones, etc. The stofen softens those lines. It's not rocket science, it actually does work. Now, distance plays into this quite a bit. If I am 20 feet away, a stofen wont make much of a difference, but if I am closer than 10 feet, I see it. It's enough of a difference for me to keep using it when necessary.
You do have to think that all of these diffusers, some gimmicks, were created for a reason. I know one of those reasons was that people were not happy with direct flash.
I have also used them in off camera flash situations where even dialed down to 1/64, the flash was too much. Rather than moving the flash further away and changing the light angle, pop on a stofen which can further reduce the output a little.