Remember the incident when the Jet Blue A320 plane was flying around the Los Angeles area with the nose wheel stuck down and sideways? While the plane was flying around to burn up fuel, the flight attendants had the passengers move themselves and their carryon baggage to the seats in the back of the plane.
That's a different situation than your normal weight and balance stuff. Another words, if this was a normal flight flown to it's originally intended destination, the passengers would not have had to move aft with their luggage as the aircraft burned up fuel during the cross-country flight. The passengers were moved to reduce weight near the front and lessen the pressure on the malfunctioning nose gear upon landing.
Just for fun, I'd like to see the pilots' reaction on a flight if I can get all the passengers on something like an A340-600 (loooooong) to run to the back of the plane all at once...