Not sure I know what you mean by being stopped. I tested all functions that I know of with the eyesight system. When the vehicle in front of me drove off, I stayed put long enough for eyesight to tell me the vehicle in front of me had gone. So if that's what you mean, then yes, it worked at stop lights.
I haven't driven with a considerable amount of snow on the road... I guess that's the best way I can put it. But I used it in some seriously heavy snow last night and it never flinched.
I wouldn't say eyesight is really abrupt at all. If you're using it in traffic around town (which Subaru advises against) then it'll be as smooth as the traffic you're in I guess. As for being on the highway, this is where eyesight shines. When you're stuck behind someone that keeps varying their speed, I don't have to constantly disengage/reengage the cruise control anymore. I don't typically notice it either. I'll have cruise set at 70mph then look down and see I'm going closer to 65mph because the car in front of me isn't maintaining a set speed.
My reference to the stop signs and stop lights was out of my curiosity of the windshield area where the stereo cameras are placed would be covered in snow. Some people have said when the sun is directly shining at you that the system has to stop operating because it can't see either. The same goes for fog.
I was wondering if, depending on the amount of snowfall and how much in a certain period of time, would temporarily require the system to shut down until the cameras could see again. But, as I was driving to work today, I noticed my Forester wipes the entire windshield to the top where EyeSight cameras would sit so that answered a part of my question.
My other concern comes when you wake up and it stopped snowing but there's snow on top of the car. I'm wonder how quickly and how often the EyeSight system shuts down or stops operating when the camera vision is interrupted. You know, like when you're coming to a stop and the snow on top of your car comes sliding forward onto your engine hood from your roof.