I did some experimenting with hyperfocal calculators for my Canon Pro1 which has a small sensor (4x crop factor). I am not an expert on this, but the hyperfocal calculation is dependent upon your tolerance for fuzzy focus. As you probably know, a photo that is printed at 4x6 has a much lower need for sharpness (larger acceptible circle of confusion) than a photo printed at 13x19. This has to do with the circle of confusion that was discussed above. With crop sensors like the 1.6x in the 20d and the 4x in a pro 1, you are in effect multiplying the focus (or fuzziness).
Put another way, the projection of fuziness from the lens remains the same, but the smaller sensor magnifies the fusiness.
printing a 4x6 photo taken with a 1.6x crop factor camera will have the aparent sharpness properties of a 5.6"x 9.6" print.
What I am surmising is that the hyperfocal calculators are using a circle of confusion number that is appropriate for a full frame sensor at a smaller print size. If you plan on printing larger prints with a crop factor, you will need to factor in a much smaller circle of confusion.
I am still formulating this understanding in my mind, but I think I have this right. Does anyone have any clarifications on my hypothesis.