It matters because she's the newest, biggest spokeswoman for the religious right and their bigotry. Her public humiliation and her exposure as a sexual hypocrite weakens her ability to hurt people in the future. And that matters.
From AP:
The directors of the Miss California USA pageant are looking into whether title holder Carrie Prejean violated her contract by working with a national group opposed to gay marriage and by posing semi-nude when she was a teenage model....
The detailed document prohibits the titular Miss California from making personal appearances, giving interviews or making commercials without permission from pageant officials. In the last 10 days, Prejean has made televised appearances at her San Diego church and on behalf of the National Organization for Marriage, a group opposed to same-sex marriage.
The contract also contains a clause asking participants to say whether they have conducted themselves "in accordance with the highest ethical and moral standards." As an example, it asks if they have ever been photographed nude or partially nude.