I used to be in the "aimbots would be dumb" camp but after playing on EU3, I'm convinced some people have them.
Very typical aimbot-type behavior:
I stand in the open, watch the archer, time his shot, then step behind the siege shield. Arrow hits the siege shield pretty much where my head would have been if the shield hadn't been in the way. I can do this with some people repeatedly. If I stay in the open they'll hit me. If I step behind the shield they'll shoot anyway.
What human archer is fast enough and smart enough to correct his angle of fire and then slow enough and dumb enough to shoot it right into a siege shield? Yet an aimbot clicker will do this all the time. It's a standard way of identifying them in FPS games.