One of the minor subplots of yesterday's U. S. Presidential Inauguration was the the goofed-up oath of office. Here's an in-depth article explaining what happened. Most important, as the article points out: although the wording of the oath is indeed specified in the U. S. Constitution, it's really just for decoration. According to the Constitution, Obama became president at 12:00 Noon, oath or no oath.
UPDATE: Some say no, you really really need to say exactly that oath, and Obama should retake the oath.