Thank you for all your replies - i will admit it is much as I expected - and will agree that if told to do something by the crew, we should always do it.
Sir Herbert, I must say, that I am told (not always politely) to turn it off, but not to put it way. With the amount of hand luggage that is taken aboard these days, I think the other pax are in far more danger of the overhead bins bursting open - I have seen people needing help to heave their 'hand luggage' into the overhead bins!