What you do and what you say should depend on how you read the person interviewing you. You can see that this is true just from the variations in responses to your post. This means that there are no hard and fast rules (IMHO) for interviewing.

A large number of interviewers have no idea what they are doing, and have no use for the questions they ask. Who knows what some of these guys base their decision on ... probably just whether or not they "liked" you.

That said, there are a few hiring managers out there that conduct quality interviews that you can feel good about. These are probably the type of guys you would rather work for anyway.

just my 2 cents ...