This is a story from Clive Grinyer, former director of design and usability for Orange. I believe he now works for the parent company, France Telecom.
Researchers working on Heathrows terminal 5 wanted to find out where people spend most of there time in an airport. They looked at all the demographics and documented their behaviour. They found that older people spent a lot of time in the toilets. The architects naturally reacted by adding unpresidented numbers of lavatories to the plans. But later...one bright spark decided to follow a group of senior citizens into the loos. He soon realised that they were not actually using the facilities, but were trying to listen to the announcements. The toilets, it seemed were the quietest place in the airport to hear the announcements.