I use the 1.4 on Nikon equipment since it was released, about 3 years ago. It is a great lens.
In terms of durability it is extremely well built. I've hauled it through deserts, exposed to sea water, had it slammed in the back of a pick-up, with no negative effects so far except a crushed hood and the expected scratches.
There is no effect on the image quality either. I originally had a Nikon 1.4 that was lighter, but the Zeiss makes things "pop" and the bokeh is very pleasing. Wide open it conserves good contrast and has soft DOF transition. In subjective "magic" terms, it seems to inherit a bit of the "clinical" sharpness of the Zeiss lenses, but the bokeh/DOF reminds me more of a summicron.
My misgivings are its size and the focus seems a little loose now, although that might be due to it's wear and tear. These are minor points really.
If you already have a 50mm that you are 80-90% content with, or if you do not use 50mm that much, I would recommend you stick with a Canon prime. If the extra stop is not too important, then the 2.0 might be better. Otherwise it really is a great lens, and half the fun is using it wide open.