Pros: Super-sharp images, Superior build quality, Fast auto-focus, great in low light
Cons: havent found any to date
Aquired this lens earlier this week WOW.! The auto focus speed is simply amazing, with both the 5D MKII and the new 7D. The optics are the best to date of anything that I've used - I believe it's better than the current Canon 300 F/2.8 and the 500 F/4. The weight isnt bad, hand-holdable for me, and the 'little white whale' works well with both the 1.4 and the 2.0 extenders.
Would highly recommend this for sports, as a second lens - in addtion to carrying a 400 or a 500.
I gave this a go an engagement (wedding) shoot. A little large, but for interior shots, in low light, this really worked well.
It utilzes the same drop in filters as the other telephotos, and I believe it may take the place of my 300, for a number of projects.
My hats off to the folks at Canon.......again!