For Douglas:
Airlines often specify that only LARGE items should be placed into the overhead lockers, with all other items being placed under the seat in front. (The only exception is where passengers are sitting by the emergency exits, where all bags have to be put into the lockers). easyJet stated exactly that on my flights to and from Amsterdam a couple of days ago.
So (with the exception of people sitting by the exits) , the correct place to put hand baggage is under the seat in front. The lockers should only be used if that's simply not possible.
From the easyJet website:
"Remember that you can stow hand baggage not just in the overhead lockers: small items must be placed underneath the seat in front."
http://www.easyjet.co...Planning/baggage.html
Chris