Interesting current thread over on DPReview...
Many focusing issues are acknowledged as typical for this lens. One person even states he's glad he has his Canon 1.2 to fall back on when necessary (imagine that!). Guess we don't have to look back to bountiful earlier threads for instances of focus issues. Why would it not be justified to be cautious regarding possible focus issues with the NEW Sigma 1.4 lens? Inquisitive rational minds want to know!
I cant speak for all copies of the 35 art obviously, but the first guy complaining about it was at f1.4 and 1/30sec. In order to pull that off, you need to be SOLID as a rock. I would consider that trash data personally. Just like that user here who was shooting at ISO 3200, f1.4 , focusing on a branch 60 feet away in a wind storm lol.