Whoops, I was right first time.....
IDmk11 has a sensor size of 28.7x19.1 mm and 8.2million pixels this is a size of 548.17 sq mm giving 14958.86 pixels per square mm, (this is much the same as the 1Ds) whereas the 10D has a sensor size of 22.7xx15.1mm at 6.3 million pixels this is an area of 342.77sq mm and yeilds 18379.6 pixels per sq mm so there is a 22% increase in the number of pixels that the 10D image offers. However the number of pixels per square millimetre does not necessarily mean a better quality image. For my money I do not feel that the 1Dmk11 will give sygnificantly better quality for the huge price difference.
There a number of technical factors relating to "Airy disc" size (also called 'circles of confusion'. This is the diameter of a point of focused light at the plane of focus, i.e. sensor) that can conspire to degrade the way the image is recorded, the cameras software fit relating to how the image in processed does also make a big difference.
The problems arising from the sensor size/pixels per square mm are also relative to the lenses used i.e the amount of depth of field a lens offers decreases as you get closer to your subject, therefore as you will need to get closer to the subject with a larger sensor sized camera, to get it to a relative size in the frame, the aperture you will need to use to get the whole subject sharp will have to be smaller (stopped down), so a higher number of pixels per square millimetre may not give a gain in image quality as the light from a point of focused detail will be spread over many pixels because the Airy disc gets bigger with smaller apertures, and these points of focused light will, for want of a better description, overlap, the image will, despite having more depth of field, be much softer.