Way back (way, way back) when I took driver's ed in highschool, I remember being taught that the correct thing to do is to honk as one passes bicycles. I don't remember the reasoning - scare them off the road? - but I do remember thinking how much I'd hate it happening to me.

Never have honked at a bicycle yet. And at this stage of my life, I doubt I ever will.

Hmmm, it would be nice to have a more friendly sound to warn of your approach. Something between a honk and a bicycle bell that wouldn't scare someone into harm's way, and at the same time letting them know you're there. Might work for kids in a school zone, too.