Shanghai kicked off the World Expo Friday by setting the skies along its riverfront ablaze with fireworks, welcoming the huge showcase of ideas, culture and technology with a bang. From the US to North Korea, a total of 189 countries will have exhibitions at the six-month event. About 20 world leaders attended the opening ceremony, including French President Nicolas Sarkozy and South Korean President Lee Myung-bak. Here are some facts about World Expos: __
