Look back: 25 great 'Oprah' moments

Australian author Rhonda Byrne's self-help book "The Secret" was published at the end of 2006, but it wasn't until Oprah had the woman on two episodes of her show that the book, its philosophy and its DVD predecessor became a media sensation. "The Secret" espouses the power of positive thinking, and Winfrey's endorsement of it raised the eyebrows of critics who lamented that she was using her vast influence to peddle something many considered to be a lot of hokum.