Currently debating which of these lens to get. The f/4 does have the advantage of being lighter, and there have been reviews that it's sharper than the f/2.8 wide open or with both at f/4.
Rather than try to tell me which is better for MY needs, I'd like to hear about your own experience with these lenses, what your requirements are of them, and how you feel they met your requirements.
Any comments about or experience with the 70-200/2.8 IS II is also more than welcome.