The interview only lasts 5 - 10 minutes generally. How can you possibly make a decision within that length of time. I agree with Carl, I think the decision is made before with the information they have at hand. If they think it might be questionable and he is not present at the consulate, blue slips are easily produced. If he shows up, then this can answer a lot of questions in their mind. I, for one, am going to be there at the interview. I felt bad for Carl when Bing got her blue slip, but I also appreciate his sharing with us so we all learn the process much better.