I never had a problem with it. People complained about the softness in the corners and also some real sample variation when the camera/lens were very newly released. So I actually did a brick wall test when I got mine (which I NEVER do!) and it was a little soft wide open, but tightened up very nicely closed down a stop or two. For the kind of shooting I do, it was never an issue, but some people are really bothered by it.
I also have a question about it which I was going to post funnily enough. Maybe less a question and more an observation. On Sun I went walkabout as I am wont to do, and came across a few lovely scenes which I tried to take nice photos of. Having the full kit with me, I took some shots with the 16mm lens and some with the Canon FD 35-70mm at various apertures. Standing in the same spot shooting the same thing at the same time the Canon pics are sort of red in hue, whereas the sony ones are green/blue. I'll post a comparison shortly.
Is that a magical science refraction type thing where the longer wavelength of the red is more prevelant in the 35-70? Or am I barking up the wrong tree altogether?
Never noticed any problems with it other than the things it is actually supposed to do like push everything a million miles into the background. Not my style. Handy trick to have up the sleeve though.