I don't do "the nod" anymore. I used to do the respectful downwards nod with a smile if I met patients in the hallway back when I worked at a hospital though, since it's part of the job (y'know, making the patients feel welcome and all, not just an "invisible" being to be treated when we feel so).
I've also stopped acknowledging people on the street (I just walk straight past with my eyes locked in position to straight-forward), since I used to throw a smile at people I didn't know if I was in a good mood, but apparently doing so is creepy...
To people I know however I do this half-arsed salute with two of my fingers (not the entire hand). It usually makes people wave back.