Sometimes interviews seem to go well when, in fact, they really haven't gone well at all. You should beware of the interview that gets too chummy. It may be that the interviewer has already decided not to hire you and out of politeness spends the remaining time talking about everything but you. The simple truth is that most initial interviews really last only about 5 minutes. But if you haven't convinced the interviewer by the 5-minute point that you're the right person for the job, it will be next to impossible to recover.
Recoveries do happen, but they're rare.
In that first 5 minutes of the interview, the interviewer will already know almost everything he wants to know about you. Your personal presence. Your eye contact. And, most important, your personality. Notice that there's no mention here of your experience, knowledge, education, or talent.