I have seen numerous loading schemes that work under controlled conditions - such as the military loading of a 747 as described by meleagertoo. But they all fail in the face of regular humans. Around 1980 I was working in a posh hotel in London's West End. The Head Porter, who had been there a long time, explained, "When they walk in the front door - their arms drop off and they can hardly carry a newspaper."
The other kind of behaviour that is unresolved is the Emergency Evacuation. I have watched those videos as they test the speed of emptying various aircraft. I am glad not to have witnessed it in real life (yet...) as I have little confidence that the 90 seconds can be met.