I nod. I've even been asked why I was so standoffish by someone who didn't know me very well. My response: "What? I nodded. Do I have to smile and wave EVERY time I see someone in the morning?" And my wife has had to actually retrain herself to stop using a nod as a morning greeting, and begin saying "Good morning" and the like. One of the downsides of moving up the ladder, I guess.
In fact, one of my biggest gripes about MMO emotes was the complete lack of understanding by game developers about what a nod actually is... A form of greeting, an acknowledgement of equal standing, and for the more flamboyant types perhaps even a tip of the hat. Yet every MMO I've traversed in my [REDACTED] years of playing, any game that puts an animation to /nod leaves my character standing there, flapping his head in agreement like an idiot.
Sure, they'll go so far as having both /clap and /golfclap, but they always make /nod the stupidest animation imaginable.