I know that the refillable mug questions always cause a big debate here, but honestly the CMs in the resorts do not police this as much as this board does.
I stayed in the CBR and the Allstar Music resorts this year and trust me I saw last years mugs being used, Blizzard Beach Mugs, and mugs that people just seem to have brought from home.
I know that the signs say good for your lenght of stay, but until Disney enforces this people are going to bring back their mugs time and time again.