Finally got around to ordering one of these this week. I wonder if Canon are gonna keep the MkII's in production too. The price difference is humonguous.
Anyway. The extender comes in the usual Canon cardboard box, with the booklets that no-one reads, and a clothlike bag thingie. Smaller version of the one you get with the 24-105L F/4.0.
The build quality is what you'dd expect for this kind of money. Like a tank.
Installing it is simple. First hook it up to the lens, then attach the camera-body. At first it goes kinda stiff, but supposedly thats due to the weathersealing.
Ill be taking it with me on a photo-trip this week. Results will be posted, offcourse.