I must say these Zeiss lenses always have that special "Zeiss characteristic" which is hard to qualify. They are really sharp and also render colors and shadows dramatically. Maybe it's just my imagination.
I feel the temptation to shoot wide open too much, but I've gotten in the habit of stopping down more, to achieve a wider depth of field. I've gotten less obsessed with the blurred background and more about other characteristics.
2.8 is still a decent aperture for low light, but 1.7 would still be better. I always feel worried if I use a 2.8 lens, that it will not be adequate if I'm using at night without a flash or indoors.
So I usually go with the 50mm in this case, but recently I got a 35mm 2.8 vivitar lens, so I will try it out and see, I haven't used 35mm much.