I subscribe to the King of Style's etiquette (lesson #4) in this department because I feel it creates a friendly sense of community.

I usually give a wave, nod, or hello to everyone (regardless of bike and also joggers/walkers). There are two exceptions. The first one is when I didn't see the person because I was messing with my water bottle or looking at my computer. The other time is when I'm riding on the bike trail by my parents' house and there are cyclists every 2 seconds (I do try to smile and nod, but saying hi every time is exhausting).

I ride alone 99% of the time. I also ride enough that I often see the same people out. I want to appear friendly enough that if I'm standing on the side of the road with a technical and they see me, they'll be kind enough to stop and ask if I need help even if I don't.

Very rarely do I ever not get a wave, nod, or hello from others. Usually the most enthusiastic greetings are from other women riding solo.