Airlines need to realize something. No one respects their authority. No one cares if the seat belt sign is on or off. They will do what they please whenever they like. It is astounding more people don't get on their cell phones minutes before landing, but it is getting there. Bags on the plane are getting larger and no one that works for the airline seems to care, or they just don't have a big enough voice to tell someone "no". Getting up at the end of the flight is getting earlier and earlier after landing.
The point though, is this. When calling people to load the plan, they really need to demand that the rules are followed. Larger flights I would guess are delayed by 20 minutes, or take 20 extra minutes to board, because people can't follow those rules. Flights that have 400 people boarding could be much efficient if people would load from the back properly. It would save people from getting backed up on the jet way and waiting 10 minutes in the aisle to sit down. Which comes back again to the carry on bag issue.
Passengers are blocking the aisle for 10 minutes to find places to put their crap away. People are loading 2 full sized bags and then adding to it video game systems purchased while on vacation, or televisions, or just about anything else you can find for cheaper in other countries or in Duty Free. On long international flights putting a bag under the seat in front of you is not a great option and filling up the overhead bins with crap is making flights uncomfortable.
This is a message to the airlines, take control with the authority that you presume to have or relinquish it all together. Pretending to have power is not helping.