This was a first for me. DL MD 88, ORD-ATL. Front cabin was full, 16 pax. Rear cabin only had 21 or 22 pax. Prior to takeoff they announced there was a weight and balance issue, and all the coach pax had to move all the way to the rear for takeoff and landing. They announced that again shortly prior to arrival at ATL, and moved them all to the back again. I've encountered that on barbie jets, but never on a real jet. Have any of you run into that, or is it really rare?