Must say that I'm one of the satisfied users ... OK, the handling irritates me at times, but the image quality is first class. With the exception of the images I'm getting from a 50mm f/1.4 lens at full aperture, which really isn't acceptable, but I'm quite happy to put that down to my particular example of the lens, not the camera.

Must say that I do not use the preview screen for evaluating image quality. I can't see the point; how is a 0.23 megapixel display without even the facility to calibrate colour going to be any use at all for evaluating 12 megapixel images? I don't even use it for deleting duffers from the memory card, just upload everything to the computer (& remove the duffers there) and reformat the card after uploading everything when it's full.

In fact, when taking pictures, I use my 5D pretty much the same way I use a film camera. I don't even bother to check exposure, just bracket when I'm unsure (like I used to with film). And I always shoot RAW so white balance etc. is fixed in the raw converter software not by the camera setting. The more I think about this, the more I'm sure this is the right approach. For me, at any rate.

Especially if you're shooting RAW ... for a number of reasons (mostly the anti-aliasing filter in front of the sensor) a certain amount of sharpening really does need to be applied, and the in-camera software isn't always the best way of applying it. OK, it works, reasonably acceptably (certainly as well as any other digital camera I've tried), but the more specialized methods such as unsharp mask with tunable parameters (available in e.g. Photoshop) and wavelet processing (available in e.g. AIP4WIN and Registax) can sharpen more without introducing unwanted artifacts.

I changed the focusing screen on my 5D to a type S precision matte screen and found it improved manual focusing considerably. In fact with the angle viewfinder I find I can usually sharpen the viewfinder image a little by manual focusing starting from the AF left off. Now lots of the images I make are through a telescope which does not have AF capability, in any case the focal ratio is too slow for the AF mechanism to work, so I have to be good at focusing manually ... I won't say it's easy, certainly not practical for action photography unless you can pre-focus on where the action is going to be, but it's not impossible either.

IMO there is nothing wrong with the AF mechanism on the 5D. It's fast and accurate enough for all reasonable purposes when used within its design limits. And changing the standard focusing screen to a type S will not cure your problem if it is caused by poor manual focusing, though it may improve your hit rate and/or make things more comfortable.