Have had the lens in a number of years and have never been really happy. The sharpness is every bit half-bad, and now I have also been affected by the notorious Err 01. Canon workshop wanted 7000 to prepare the aperture, a new cost 1 penny less at time of writing. Now, I will buy a 24-70 instead then I always have with my fast 100mm / f2.8.
The thing to hear that I have seen a hundred people who have had exactly the same problem with the lens. Most seem to have bought his over the same period. Canon refuses to admit that it is a manufacturing defect, and everyone gets put out good money to repair it. Not OK.