I have owned three copies, because I couldn't decide between the 85 L and the 70-200.
I have had one copy that was completely useless, I had it in for repair, they changed TWO AF-moduls and TWO IS-units, they took out the front end, and three glass-elements and re-aligned the glass and when it came back the AF worked perfectly, but the IS was still not starting as quick as the previous copy, and it jumped, and often worked only one direction, and made a very weird, loud noise. It was VERY soft at 200 when I sent it in, and after all the re-alignment of the glass and front end it came back exactly the same. I sold it for cheap and had the buyer try it to see if if he liked it, and he bought, so I got a third copy, which like the two others had the issue of IS not being perfect, sometimes too slow to start, sometimes only one direction stabilized. But the AF and sharpness and overall image quality and build is as good as it gets. Wonderful lens. Just not as good as the 200 L, which is the reason I no longer have it