Those 2.8 70-200 lenses are beasts - 1.3kg or more just in the lens! I don't think I could walk around with one of those all day, even if the image quality was worth it. My 7D with a lens that weighs half as much (15-85 or Tamron 70-300VC) is well over 1kg, and I can feel every gram of that once I've been going around for a while. I wouldn't want to make my rig any heavier than that, to be honest. I suppose if I was making money off my photography I'd be singing a different tune, but as an amateur I'm willing to give up a little image quality for lower cost and lower weight.
