"Why are you concerned about someone hijacking a plane and crashing it into a building? Since 9/11, if someone attempts to hijack a plane, no passenger is going to sit idly by and let the pilot and crew handle the situation. The hijacker would be attacked by the angry passengers. If the hijacker is lucky, he or she might survive the ordeal long enough to stand trial."
Thus (by my inference of boxley's post), you're safer now than you were before 9/11 due to increased vigilance by your fellow passengers - not due to the actions or statements by Department of Homeland Security.
HTH.
Cheers,
Scott.