At what age do people start thanking bus drivers for taking them to their destination? It was a question I posed to colleagues in an ad agency this week.
One suggestion was that the phenomenon had a yokel flavour and that the correct pronunciation was "thank you droiverr", but I've seen it a lot in London too. Mainly from people who were born before 1955.
It may be that the practice will die out. On the other hand, it's possible that there's an age when you just naturally start doing it.