Over the last decades, tourism has become a key sector in the world economy: its contribution to balance of payments, incomes and employment has significantly increased over time. While in 1950 international tourism receipts totaled about 2 billion dollars, by 2006 this value had reached 735 billion dollars - about 2 billion dollars a day (World Tourism Barometer, 2007). Nowadays, the sector originates more than one third of world exports of services and over 70 per cent of those in the poorest countries (European Commission, 2007). Tourism is therefore an important driver of growth and...