I ride by a YWCA shelter each day as part of my commute. During the school year, there are quite a few kids gathered each morning waiting for their bus. I notice many of them staring at me as I ride by then turn down the street in front of them. One day one of those kids yelled "Cool bike, man!". I just smiled, gave the kids a thumbs up and said thanks. I think that also increased my speed by 1 or 2 mph.

I've had a few lectures about having bikes on streets, but it's always nice when people greet me, or just wave when I'm on my commute.