... And the remarkable thing is that there are actually professional cameras and flashes which are about 50% bigger than the 5D2 and the 580EX2 on the left!
The Lightsphere feels good, won't break (soft plastic), and does a good job.
Just got the 580EX II today, it is very nice also. It is Canons biggest, and it is actually remarkable that for the power it has, it's not bigger physically (and less than half a kilo), and still only uses 4 AA batteries, and doesn't even drain them fast, I'm told.
My early impression is that this flash and defuser is a powerful and flexible combo, and even easy to use, simply put everything on auto, and the camera adjust things so they usually look very nice.
My apartment has pretty low ceilings, so with the top left off the LightSphere the top-light was pretty overbearing in many test-pictures, but it helped a lot when I put in the "dome", which concentrates a greater percentage of the light out through the diffuser itself. And Gary Fong had indeed said that this was its use.
Below is a sample of how the diffuser softens the light, and the camera/flash automatically balances the light, making the whole thing look very natural. Before flash-metering through the lens, it was a difficult procedure to balance flash and daylight. (And with film you did not have an instant preview of course.)
I had to find data on it on the net (google is my friend), for it seemed the auto-zoom did not work, but now it does. And it's just so cool to zoom the lens and have the flash zoom automatically follow it! I really didn't know they could do that.