Summary: I have been using this lens for a couple of months. It is the best lens that I have owned. I use it with my Sony a65. As an amateur I have been learning my craft and this lens has made a huge difference. There are plenty of reviews on the technical side, so I wanted to express the fact that this lens will up anyone's game and provide beautiful images.
Summary: This lens is the pinnacle of technology and optical quality for portrait artists. Though a bit on the heavy side for use on mirrorless A7R but I have not taken this lens off my camera ever since i received it. Images are rendered beautifully and the bokeh at f/1.8 is amazing. The image center is very sharp when used wide open and creates incredible pictures.
Summary: I bought this lens in mid December, 2013, and I have been stunned by the quality of the photos I have taken with it. It took some getting used to. It is big and heavy, but I love that about it. Sometimes it doesn't focus quickly enough and occasionally it tends to hunt in very low light, but with this lens, when you nail a shot, you knock it out of the park!!! I love it and I use it every chance I get.
Summary: I'm not jumping on the bandwagon with this lens because its a Zeiss. I have used this lens a couple of times with mixed results. I had taken this lens out one day and popped it on my A77 for a Parade local in my area. I would say about just less then half my shots were good and usable. The day was overcast but i was still able to attain fast shutter speeds and low ISO using a 2.0 or 2.5 aperture for the day.
Summary: Not much else I can say that others haven't, it's a fantastic lens. Not a negative point about it, but something to keep in mind is that 135mm isn't at all wide-angle. You really need to be prepared to move back physically to get the desired shot.