Heh. Calling out "Passing!" deserves it's own entire debate thread! I've given up on doing that, since I inevitably either:

1. Startle the living daylights out of the person in front of me, with resultant unpredictable behaviors ensuing, or...
2. Am totally defeated by the earbuds of the person in front of me, who might not even notice if that Russian Meteorite were to explode right above their heads.

Now I just slow WAY down and pass them quietly at near walking speed, with as much distance between them and myself as possible. Unless they're walking a dog.

The "not noticing, even with the mirror" thing is common for me, since the mirror only alerts me when I think to look at it, and my hearing sucks, so modern quiet cars still get right up on me before I hear them.