Yesterday, General Patraeus gave a brief talk and took questions. What's interesting is how he responded to questions. People often ask gotcha questions, in effect the proverbial, when will you stop beating your wife. So someone asked about executive initiated wars and their legality--I am sure I am misrepresenting the question. Petraeus proceeded to answer in a highly professional manner, indicating his awareness of the legality issues, the procedures he follows, and also distinguished differences of policy (the executive is in charge) and in carrying it out. I watched him handle a discussion of what went wrong under Bremer's regime in Iraq, so that he said nothing bad about Bremer or the White House, but also indicated how things went awry.
You could say that Petraeus was avoiding the questions. My own view is rather that he is giving his perspective as a professional soldier. Surely he knows who did what and who was wrong, often enough. But as a soldier who understands civil-military relations he knows where he stands and what he is responsible for. By the way, if you read memoirs by Rumsfeld or Rice, you won't find this sort of tone--they are always not responsible, or no one told them or disagreed at the time with their policies and actions. So what is interesting is how Petraeus articulates his soldier position. And how he distinguishes the role of a two-star (general) from his role as a four-star.
I treat such speakers as evidentiary or exemplary. The questions you ask them are meant to elicit their own sense of the world. They are much too smooth (they don't get to be four-stars if they are not) to be tripped up, except perhaps in a Congressional hearing, where senators have the ability to follow-up their questions, and set up those beating-your-wife questions. Or, in situations, where an expert shows that you are wearing the emperor's new clothes, or misrepresenting what happened.
In seminars, I try to ask questions to figure out what's going on. Rarely, if ever, do I know enough to find the hidden flaw in the research. But I really do want to find out what's up, the motivations, the take-home from the work. It's easy to satisfy me, and if you say the right stuff in the first ten minutes of your talk, I am quite happy to just listen (or leave). But it is often difficult to find out what's going on, even if you ask those questions.