How about what side of the road you drive on.
Knights rode on the left so that their jousting lance was in place to take out the opposition, or walked on the left so their sword arm was nearest to any enemies coming the other way.
But this began to change when the french, and left handed leader, Napoleon rose to power. He needed to pass people on the right so that his sword arm was ready for use. This was adopted throughout the French Empire.
Fast forward to today, and roughly three quarters of the world drive on the right. Go Napoleon!
Famous left handers include Winston Churchill, Angelina Jolie, Julian Clary (whose autobiography I always attempt to read when we pop round to see my fiancée's mother - I'm about halfway through) and Prince William, who is about a month older than me.
As an aside, I got this particularly interesting spam comment on one of my blogs the other day...
I have a notable synthetic eyesight pertaining to fine detail and can anticipate troubles just before they occur.
Really! Thanks for that! I'd quite like a superpower too. Perhaps "I am able to decimate ten pies in five minutes"?