What have you changed your mind about?

Every year Edge asks a question, and gets leading brains and professionals from every field answer it. The results take you far out of your own mind and world and let you catch a glimpse of the wheels that turn the world. Or they just give you new things to argue about with your friends. Either way, the 2008 question has been unveiled:

What have you changed your mind about?

Check out previous years' questions here. I was particularly a fan of "What do you believe is true even though you cannot prove it?" in 2005.