Cameraclicker, I’m going to disagree with you saying that it doesn’t affect DOF. Try punching some numbers into a dof calculator and you’ll see what I mean.
You are always free to disagree. I think the DOF calculators I have seen, such as http://www.dofmaster.com/dofjs.html, are flawed. When I use them, I generally use the 1Ds body selection because I think it is most accurate. Playing with the calculator is a nice academic exercise. In the real world, cameras have a button that stops down the lens so you can see the DOF as you are working.
When I got into digital, sales people and some of the forums had a lot to say about the “magic” crop factor. My own testing suggests it was a lot of nonsense. I have put some notes here: http://cameraclicker.com/Compare/Sensors/Sensors.html, and here: http://cameraclicker.com/Compare/DOF/DepthOfField.html.
I tried crop and full frame bodies through the same 150 mm lens mounted on a tripod using the lens’ mounting foot. The results are at the bottom of the second link to my page, above. I don’t see the difference the DOF calculator predicts. I chose the Sigma 150 mm macro lens because longer lenses show DOF more readily than short lenses and that lens has a foot for the tripod so I could remove one body and attach another without moving lens or tripod, ensuring distances remain constant. If you think I should do the test differently, feel free to suggest how to do a test. I have a collection of lenses and four bodies, two crop and two full frame to perform a test with.