Yes I have reason to believe that mine was not the only "bad sensor" out there in Mk2s. Afashionshooter.com went through several cameras and I have been in touch with him... only his recent one has been good, the early ones were problematic.
Daan, I have noticed a huge difference with the new sensor. Noise is much more controlled or eliminated, there is a nice smoothness to the files, and the tonal transitions are now beautiful - basically what I had expected from the Mk2 but was disappointed with in the first sensor.
I was beginning to think I was crazy - I had exchanged emails and images with Chuck Westfall and he didn't seem to see the IQ issues I was seeing, and then when I took the camera in the counter person was looking at me really funny when I explained some of the problems.
I think for those of you who feel the IQ is not quite there, send it in to Canon so they can check to see if it is up to spec.