http://www.superbowl.com/news/story/9190135
Terrorist would love to attack the Superbowl. However, they will not. I cannot see them taking such a risk on a day when security will be so high. They have always hit us when we least expect it, when they have a better chance to succeed.. The Superbowl will be safe.. Security measures are planned years before the event even takes place.. Arizona has already been planning for security for the 2008 Superbowl.
It is not to say an attack could not happen somewhere else on that day to draw attention away from the game.. but i think one of the safest places to be that day will be in Detroit.