There is a lot of rubbish about this glass on the web. I love mine, never ever had any dramas with autofocus this or tha, mind you I use it on 1Ds mk3 ( two diff bodies) and both are perfect and tack sharp whereever you point the selected focus point...
I'm attaching couple examples
First shot was focused on the "OU" of the last word, note that on this trip to this nice place on the mountains it was pissing down all day, did I care
Not at all since the lens is weather sealed.
Second was shot whilst walking next to my wife, focused on my daughter's eyes, any sharper it would cut my screen in half
Buy it RIGHT NOW !!!
I can send you the RAW files if you want to have a look at them, however I can guarantee you, for what you want, this piece of gorgeous glass is unbeatable.