Quite Interesting one of the most Interesting quizzes that have come to this planet through the television that is our centre of knowledge, mentioned this. They asked what the number of the beast was and Alan Davies who got it wrong (as always) got a bunch of negative points for answering 666.
Their story was that it was originally 616 but was then afterwards translated wrongly into 666 by a man who thought it would be 'simpler'.
It's pure superstition, of course, so I kind-of cringe when I heard the Europarlement has nobody sitting in chair 666 - though that may be a silly story.
And interestingly enough the fear of 666, which by definition is a phobia as it has no real ground, is called 'Hexakosioihexekontahexaphobia'. People who are afraid of long words should never go to a psychiatrist when unnerved with the number 666.