I use the 14L, and you'll find vignetting and distortion at full aperture. Stop down and the vignetting clears up quickly, but the distortion's there for keeps!
Overall it's a good lens, very sharp in the centre and reasonably sharp out towards the edges. I compared it once to a much cheaper Voigtlander 15mm on a Leica and the Voigtlander was noticeably superior, but if you want digital and especially full frame digital then there's few alternatives.
It's bulky, heavy, and expensive. But at the end of the day it delivers the ultra wide-angle impact that drives sales from libraries and that clients always seem to demand.
