Some notes on perceived image quality are appropriate here. First, images shot with the EOS-1D Mark IV tend to reveal blur and defocus more easily than images shot with the EOS-1D Mark III or EOS-1D Mark II, especially when viewed at the same size (for example, when viewing at 100% on a computer monitor). After all, the EOS-1D Mark IV provides 16.1 Megapixels — approximately 1.6 times more than the EOS-1D
Mark III (10.1 Megapixels) and approximately 2 times more than the EOS-1D Mark II (8.2 Megapixels).

As long as final print size is the same, the visible effects of blur and defocus are the same regardless of pixel count. However, it is becoming popular to view images on computer monitors; thus, clients and photographers are increasingly concerned about blur and defocus in images shot with high-resolution cameras. EOS-1D Mark II and EOS-1D Mark III users should understand the increased likelihood of blur and/or defocus when using high resolution cameras. To prevent these image defects, photographers should use faster shutter speeds at high ISO settings and/or shoot with IS (Image Stabilizer) lenses.

That, alone, made this whitepaper worth reading, I think. Remember everyone, as megapixels go up, the stuff you see at a 1:1 level will be increasingly flawed, and that decisions regarding ultimate image quality can only rationally be made at the proper final viewing size. It’ll save you a lot of frustration with your equipment if you keep that in mind.