you are not a constitution attorney I afraid

The courts would probably never hear a challenge, and some might argue that Obama automatically took office at noon because that's when President Bush left the office. But because the procedure is so explicitly prescribed in the Constitution, if I were Obama's lawyer, I would recommend retaking it, just as two previous presidents, Calvin Coolidge and Chester Arthur, did under similar circumstances.

The Constitution says what he's supposed to say.

The only reason not to retake the oath would be to prevent further embarrassment of the chief justice. It would seem appropriate for the president of the United States to take the oath specified in the Constitution.