Actually I forgot to mention that is it mostly the case for taillights (the most noticeable since you're going to follow cars quite often) and accent lights (like the vertical strips on the front of recent Peugeot cars).

Not really on headlights I guess so I might be off-topic. And although I understand how some people can find it annoying, I don't really mind them. But I can definitely see the flicker and can compare the duty cycle between different cars.