I am not a technical guy so graphs and charts dun work for me..... i bought the 70-200 f2.8L since sep '06 and never looked back. Punchy colours, great contrast, sharp images and beautiful bokeh.... and the USM is fast and silent. In fact, the images are so good that i tell myself not to buy another len unless it is L. (I went on to buy the 28-70 f2.8L last week....)
I also like the fact that it is f2.8. May be beacuse i migrated from a f3.5-6.3, i like the fact that there are min hunting under low light. I find the weight manageable (I am not particularly big fellow), and the IS a godsent.
Down side: Other than the hefty price tag, I dun like the fact that it is WHITE... it simply attract too much attention, esp when u have the hood on (I Always have it on), it looks... BIG

I also dun like the tripod collar: it cannot be removed unless u remove the lens from the body. And firing away with it in position hinda hinder the holding. (But u can rotate it away to the right, away from your left hand). Some do complaint of noisy IS but I find mine quite ok.
Overall verdict: Great lens.. worth (in my opinion) every cent of it. Well built delivers. Go get one if u r planning so already....
Hope this helps