Conclusion: For this price, I would expect a much better lens. Sharpness is very poor at the frame corners, unless you stop down to at least f/2,8. Vignetting is as visible as in much cheaper and older lenses. Built quality is excellent and distortion is very well controlled, but that's not enough to justify this price. At present, the 24/2,8 IS is probably a better purchase for most people.
Conclusion: I am using this lens with my 5D Mark II. There are AF issues with the lens out of the box. Probably 80% of my images missed focus. I have the precision screen- so I can see the AF locks at regions that are not correct- even at high contrast regions (e.g. keyboard) This is a bit fustrating because when I use manual focus- the lens is amazing. I own the 35 1.4L, which did not have this problem. The issue is not backfocus or frontal focus problems- I cant never know!
Conclusion: I just got this lens and put it through its paces on my 5D Mark II. The first few test shots seemed very blurry, so I went to manual focus. I was then impressed with the lens. Only just a touch of softness at 1.4, and only a bit of chromatic aberration in the corners that I could see. Then I went to figure out why I wasn't getting good focus. Sadly, I could not resolve this issue.