The debate format is a valuable tool. You soon learn who you can debate, and the type of person who debating with will be fruitless. Dawkins won't debate with creationists. It helps you develope your arguments, it does change minds, and you can usually find some common ground.
Sam Harris and Andrew Sullivan are having an informal debate, it follows somewhat like a debate format.
Dawkins and Hitchens debate theists about the harm of religion.
