Very good image quality.
My copy is very, very sharp even wide open. While I haven't done any direct comparisons yet, it is my believe it is nearly or as sharp as my 85L II.
Great colours and contrast, as long as you don't shoot with it in the direction of the sun. If you do, it will flare badly and contrast will go down the drain. In some occasions (portraits), it can be a desired effect, though.
DOF is very thin and getting the shot focused exactly where you want can be troublesome, even using the 7d's spot AF.
However, since it's a 50mm lens, background blur is not as evident despite the very large aperture and razor thin DOF. I have portraits taken with my 500mm f4IS that have more background blur than the 50mm 1.0 wide open, yet DOF is larger (most of the face in focus).
The bokeh can be very nervous under certain circumstances.
And in some occasions, the background will have a swirling look to it, giving the appearance of circular motion.
I love when this happens, since it gives a very distinctive look to the pic. It's the lens unique signature.
Wouldn't want it in every pic, though... :D
It's hard to use it wide open outside. Since it lets in so much light, you will go over the 1/8000 SS limit very easily, even at iso 100.
All in all, a fantastic lens.
My only complaints would be the price and the sluggish AF.
At least it's faster than the 85L II!
Highly recommended if you can get a sharp copy (unfortunately it seems there aren't many...)