My last point (to all of you horn-lovers [smiley=2vrolijk_08.gif]) is that in all of these cases, by the time the horn is effective, the incident is already underway. As a rider, you have made one or more mistakes, and so has the other driver. (Haven't we all??)
A preemptive approach avoiding cases where you're riding or driving next to someone is much more effective.
In other words, the safest way to ride is to not get into these situations in the first place, rather than waiting till the last second and hoping the horn will get someone's attention.
This is the difference between a passive safety device (horns, lights, hi viz, "loud pipes") and an active safety device (brain + eyeballs + intuition + prediction, throttle, brakes).
With a passive safety device you're relying on someone else noticing (and caring) and being able to change the situation. The last place I want to put my life is in someone else's hands. The active approach puts control where it belongs: with the rider.
Of course, horns and all that have a place, they're not completely worthless. And naturally I wear a full helmet, gloves, boots, and an armoured jacket every time out. But leaving my safety to someone else is a non starter.