I was on an Air UK Shorts 330 flight between Amsterdam and Leeds some years ago and was asked to move to the front for take off and landing. I am relatively heavy and the stewardess explained that it was a queston of trim and weight and balance. As I have a Private Pilots license, I knew what they were talking about and complied...not without a grin though.

Also, a long time ago I was flying non-rev on a Continental flight from Guam to Honolulu (DC10). I was seated in First sipping my orange juice and feeling quite happy with myself. (I had been turned down for a flight two nights in a row). The gate agent comes on board and says: "Mr. Brandt? Could you deplane please, we have a weight problem." Well...you should have seen the faces of the people around me. Of course I went, but I remarked: "Boy, I knew I was heavy, but I didn't know it was THAT bad!".