I just posted my thinking up on BF but thought I'd put it here too -
If I take a shot with a 1DsmkII it's full frame at 16.7mp, if I then crop the image to 1.3x then I get left with ~9.8mp (mich is roughly what a 1DmkIII gives) but if cropped to 1.6x I'd be left with ~6.5mp (basically what the old 300D gave). If I took the same shot with the same lens with each of these three bodies then I would need the same shutter speed to eliminate camera shake. The central portion of the three images should be the same, the larger sensors purely record more data around the edges. So by my thinkng crop factor cannot have any effect on the shutter speed you need to eliminate camera shake. (I'm not sure that I made my thinkng any clearer with that).
The focal length=shutter speed rule can only ever be a guide, personally I can get away with slower shutter speeds. When I had then 400 f5.6 I was happy to handhold down to 1/200th and at times slower.
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