I look at it this way. If you are accountable you have the ultimate responsibility for the decision or task. You have decision making authority. If you are responsible you are concerned with how the task or activity will be completed to support the decision. When you talk about RACI Diagrams, only one person is accountable to ensure that there's no ambiguity. But one or more people can be responsible for the execution. Sometimes on small projects the PM might be both accountable and responsible, but typically they would find themselves more in the accountable category.
Kyle
