It has happened several times to FedEx. With the ex-flying tigers 747, their own dc10, 727 and Airbus (dont know if it was 300 or 310). I think the record lies with the groundcrew in Anchorage: they have tipped several.
Saw it once, myself. A 727 (NB in EKCH) loaded from the rear lifted the nosewheel 10'' of the ground, but was stopped by the rear stairs. The fwd door got stuck against the ceiling of the jetty - rather messy.
PC