Yes, Christina Aguilera forgot the words to the national anthem. At the Super Bowl. In front of an estimated 106 million viewers. The "twilight's last gleaming" line came twice, and the "ramparts" never made it in at all. But give her a break, didn't she hold that last note well? In any case, even though everyone already criticized her on their social-networking platform of choice, Aguilera has issued a statement (via the Guardian) apologizing for her miscue:

"I can only hope that everyone could feel my love for this country and that the true spirit of its anthem still came through."
As to why she botched those lyrics in the first place? The Daily Mail has a theory: "[Her] error matches one that used to exist on the Wikipedia entry for the Star Spangled Banner Lyrics." If that's the case, she certainly isn't the first to be tricked by Wikipedia.