I brought the 1Ds mk3 to the service center (JAS-Tekniikka) in my hometown on Monday, and got it back today. I also discussed about the adjustments and other general things with the technician. Summary (as I understood it):
- The upgrade is about storing new low-level tuning parameters for the AF system on the camera. These tunings are normally found using Canon's special tuning tool/software, but now Canon have upgraded the tool to provide better AF tuning parameters for the camera.
- Mechanical adjustments not needed, unless something was wrong to begin with. In my case, such adjustments were not needed.
- I was also informed that the mechanical mirror-related problems that plagued some of the 1D mk3's were corrected before the 1Ds mk3's mirror box assembly was mass produced, meaning that those problems are indeed unique to the 1D mk3. Previously, I also heard one of them mention that the original mechanical 1D mk3 fault could be seen with bare eyes when shooting a rapid burst and looking into the mirror box at the same time (maybe not while it was still mounted in the camera, though - I don't know).
I also asked about the fact that I have occasionally heard the mirror in my camera return a bit more slowly than usual... as if there were a slight delay between the shutter and the mirror flipping back. I was concerned about this being an indication of something being "almost" stuck in there. Anyway, they replied that there are multiple sensors inside the mechanism that would store error codes into memory in case something was wrong, but no such indications were found.