Micro-blogging site has 500 million users - not all of them from China

Many Chinese people turn to sina weibo for heated debates or simply to air their views and grievances - and some expats are turning to China's most popular micro blog to get involved in Chinese society.

"I didn't really follow any discussions at the beginning, it was all too confusing, but weibo has become a window to Chinese society," said Christoph Rehage, a 32-year-old graduate student from Germany who majored in Mandarin at the Beijing Film Academy.