Got this lens on loan from CPS - day 1 1st impressions: after you get used to the massive and awkwardness of this lens, its most impressive. I opted to lug it around without anything other than the camera strap and the lens strap. I had a 3/8" threaded handle from a ZOOM H4N hand held 4 track recorder (looks like a cone) that I mounted in the female threaded foot. I wouldn't dare hoist the lens up with my left hand by that cone shaped handle, but with the assistance of my right hand under the lens and left on the vertical handle it made it fairly easy to hand maneuver and obtain birding photos.
Here's a few all handheld on IS Mode 1 of 3, Manual, AF, faithful mode at 1/500, F4.5 or 6.3 with Auto ISO which averaged at 1000 across these 3 photos. The AF was on Expansion or Zone AF with AI Servo enabled.
Golden-crowned-Sparrow (11453) by Revup67, on Flickr
Northern Mockingbird (11466) by Revup67, on Flickr
House Finch (female) 11469 by Revup67, on Flickr
Very impressive. So sharp with nice detail and great bokeh.