I looked and I don't see anything. Of course, lately Seattle hasn't had a lot of blue skies, but, still I did find a blue sky and I didn't find vignetting. If it's there, it's really, really , really slight.
I really like the wide angle b-28. So nice for taking pics of large groups or landscapes.
I will say that if you use a TCON-17, giving you 17X optical zoom that you need to be very careful to hold the camera steady even in moderate light. Otherwise, there is blur.
But, for the money, I think this is a pretty good camera. Also takes good videos.