When I worked in a hostel in Britain, it was the law for us to take passport numbers. I dont know why exactly, I dont believe we reported them. Though it did come in handy several times when the police came by looking for someone...
"All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find that it was vanity: but the dreamers of the day are dangerous men, for they may act their dreams with open eyes, to make it possible. This I did."
-T.E. Lawrence, Seven Pillars of Wisdom