Well, I took my 300 2.8 IS out to day, but the jury is still out on how I feel about it.
Some shots were nice, most sucked! But, I know when I first took out my 400 5.6 I hated it. I am guessing there will be a learning curve on this too, figuring out what camera settings work best. I found my self using it wide open or close to it all day, but I think that was a mistake, my DOF was so narrow, I think I was missing that perfect focus.
But, nice controlled shots like these, were very sharp, but keep in mind, I do all my editing in dpp.