many people have a problem with sensor allignment and some are also reporting focusing problems. It is hard at this point to tell if the focus problems have any truth to them. But I would wait and see.
I've had mine for about a month and have not had any problems with the autofocus or prism alignment. There were some early issues with banding that was fixed with the most recent firmware update (my camera came loaded with this update). The IQ is awesome. I've had the original 1Ds and the 1Ds II and I wouldn't trade this camera for the two combined. I tested all my lenses for focus alignment and all were within such tight tolerances that I didn't need to make any in-camera adjustments. That wasn't the case with my 1D III when I first got it back in the summer of '07 before the sub-mirror fix. I had to adjust every one of my lenses in-camera! Once I received it back from Canon with the sub-mirror fix and new firmware I have the same great focus with all my lenses as with my 1Ds III!
i've had the 1ds3 for three months, and the camera has performed flawlessly from day one. i have not had a viewfinder alignment issue, nor have i experienced any banding. i have also not needed to make any micro adjustments to any of my lenses.
the image quality is stellar, the files are superb, the metering is greatly improved as is the user interface....
I have just gotten mine 2 days ago and it's like having my honeymoon all over. I can't find anything wrong with "her". I did much reading and I don't recall any with focus issues. Viewfinder alignment, some had but sensor alignment?
In any case life is short so go get it if you can find one.
The few people I know who got theirs are very happy with it. The biggest gripe I have is that it's still unavailable for the rest of us. Canon needs to ship 200 units asp to Sweden