I acknowledge everyone as long as my current condition allows it, didn't see many other cyclists at first, a lot more now weather has improved. Reactions are a mixed bag, but most respond, though some roadies with alarm. I think I confuse them, at a distance, hunched over, in lycra and holding the sides of my butterfly bars, I'm sure they can make a judgement error, unless I have a pannier on. The blanks I've had have been predominately roadies but the most pleasant have also been roadies.
To be fair, if it gets much busier, I may give up on it, couldn't imagine trying to acknowledge all the folks on a city commute.
Scalped a guy on a MTB last week going up hill, country road, lights at the top, said hello on way past. I'm waiting on lights and he comes past, goes up grass verge(no pavement), round cars and through the reds. I scalped him again tonight, same hill, didn't speak to him this time, and lights were with me at the top.