Edwin Loring, Management Consultant, Netherlands
RACI can be utilized in constructing an authority matrix when dealing with projects AND processes.
In using it for the corporate level, I would first define your corporate processes followed by attaching a RACI to the process definition.
Thus, when people say it is used for projects quite frankly that is true, but not the whole truth. It is just as often used in process descriptions. This applies to a strategic, tactical or operational level in my opinion.
Hopefully my comment is of use to you.