Karen Nakamura mentioned that there was conversation on an EOS mailing list about the new 5Ds vignetting excessively with wide angle lenses. She pointed to an example.

Below is a shot of the profoundly unimaginative courtyard in front of my building shot at 16mm, first at f/2.8, then at f/5.6.

f/2.8

f/5.6

The lens is a Canon 16-35 L. The vignetting is visible, but I'm not sure if it is much different than I'd see on film (I've never shot film with this lens). Very wide zooms do vignette.