Great to hear about it! I was just confused between the tokino 16-28mm f2.8 and this one! I didn't consider 14-24mm f2.8 for it is being costly and a very narrow focal range.
I agree, if you take shoot @ 16mm f4, it is expected to have a softness around the corner. But I would expect it to give a sharper image when I step down to f8 and more... In some reviews, they had mentioned at 16mm f16, the images are softer at the corners. How about Chromatic Aberration?
Is it easier to correct the distortion using LightRoom 4? I need to learn about it, since I don't do much post processing except for the cropping and the color saturation.