Do I correctly recall an incident at Gatwick years ago involving an A320 or 757 inbound from some holiday spot? The aircraft dropped half the passengers at Gatwick and was then taking the rest to Manchester. The Man people were mostly seated towards the back so the crew asked some of them to move forward. Unbeknown to the flight deck, most of those people then returned to their original seats. As it accelerated, the aircraft felt as though it was prematurely rotating so the crew abandoned take off - and then discovered the imbalance in the cabin!
Think I saw that tale in Pilot..