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The 70-200IS II spends all winter on my 7D. I took the foot off as soon as I got the lens, and I don't think it has ever been back on.
I dangle the body with lens off my neck, off my shoulder, or in one hand by the grip/hand strap with the lens unsupported. I don't even think about it. I usually do the same thing with the 100-400 too. Never had any problems operating this way, be it on a 10D, 30D, 40D, and now the 7D.
I wouldn't worry about it, at least on a magnesium body camera.