Testing this lens for some colleagues... I'm so jealous.

It has great reach, very fast AF, stabilization that works very well and is sharp. In my experience it performs very similarly to the more expensive (and very white) Canon 100-400mm -- for those of you familiar with the "C" side of the universe. Compared to my Nikon 70-300mm it has significantly better (longer reach -- who buys a tele for the short end?), the AF is a bit faster and sharpness is just as good if not better for the entire overlapping range.