I received this lens through the mail on 5/28. It would auto focus only part of the time mounted on my 20D, but seemed quite sharp. Sent it to Sigma for repairs on 5/31. Asked that they fix this lens as I did not want a new copy that might do the same thing. They got it on 6/3, fixed it and sent it back to me on 6/6. I got it today. It seems to focus all the time and is still nice and sharp. Their tech's note sez that they "replaced the mainflex board". I'm satisfied with the quick turn-around. Will have to shoot a few more test photos tomorrow to check sharpness again.