I've owned the Sony A7 for about 3 months now, and I was using it with the Canon "Nifty 50" that I got from Last Suspect up until a week ago, when I finally decided to visit the camera shop and pick up the Ziess 35mm 2.8, which I was reluctant to do because of the price, but boy, has it been worth it.
The build quality is awesome - a total 5/5 rating for me. The metal elements, smooth MF ring, and Ziess branding are all very nice aesthetic additions. The autofocus is extremely fast and I was fine with shooting at the largest of 2.8, mostly because of the A7's high ISO range. Also, there is a certain added benefit to having a Sony Lens. I found the Canon 50mm really dark around the edges, and I have a lot of control over that.
The lens takes really nice on the fly AF shots, with many of them (including the above) being taken one handed. It handles lights really well, and I enjoy the lens flares. The photo of me with the headphones was taken by my Dad, who has little to no photography experience. Shooting with the lens is an absolute pleasure, it's not too heavy, it fits well on the camera, and the shots are beautiful. Cheers, Sony.
This review was not commissioned or paid for in any way by Sony.