I have been considering buying the 50D as an upgrade for my 30D (perpetually a tweener, I am), so I have been following this closely. As a matter of fact, I was unfortunate enough to jump into the DPReview forum scrum. I had a couple of observations:
The results comparing resolution crops between DPP, ACR, Zoom Browser and jpg were a big part of the problem. The moire effect on the original ACR version was very bad. I happened to still have a browser window open to the old image after they updated the images, so I saved copies. Here they are:
Original ACR 4.6 RC Version
Updated ACR 4.6 Version
This would have set off alarm bells with me when I saw it. They claimed that they updated all the RAW images in the review, but I am skeptical.
DPReview also observed that the Dynamic range performance was worse than the 40D. They based this on a magenta shift in the highlights although the 50D's actual range was wider than the 40D's. I am very curious if that same magenta shift in highlights would be observed in conversion using DPP. I would really like it if they released their RAW images. That would seem to put this all to rest.
As for resolution at 15MP, I am a bit disappointed. I agree that it probably would have been better to stick with 12MP. It does appear that the 50D gets a bit more detail in some circumstances. I spent some time reviewing their test shots and found that focus was a bit off in places, so the resolution improvement could be seen more clearly in parts of the image that they didn't enlarge. Most notable difference was visible in the text that runs vertically on the side of the middle bottle on their standard test image.
Arghh...but I am getting into the peeping. The 50D seems to have marginally the same image quality performance as the 40D with some areas that are a gnats @ss better and others that are the same amount worse, all with the extra gift of larger file sizes (CF card manufacturers and hard drive manufacturers will rejoice). But, the usability features included in the 50D are pretty nice upgrades, particularly the screen and ability to magnify on the screen to check focus.
As for the disappointment over the lack of improvement in image quality (high ISO, resolution, dynamic range) I suspect that we haven't heard the end of improvements to RAW file handling for this camera.
What I think what we have is a decent 12MP camera stretched out onto a 15MP sensor. I will need to do my own at-home tests to decide how large I can print with this camera. I may not be able to apply my simple algorithm where I take the pixel dimensions and divide by 240 to decide my maximum image size.