"Preferred rooms" are the ones that used to be requested all the time because they were closest to the main buildings and didn't require as much walking to get to food or the bus. Disney has decided to make a guaranteed reservation in the buildings containing these rooms part of the reservation process, for an extra per-night fee.
The only extra charges for "preferred rooms" right now are:
All Star Sports: Surfs Up buildings, $10/night
All Star Music: Calypso buildings, $10 night
All Star Movies: Fantasia buildings, $10/night
Starting in 2004:
Caribbean Beach: Martinique or Trinidad North sections, $15/night
I'm sure there will be preferred buildings at Pop Century, but I don't know what they are.
There aren't any "preferred buildings" in deluxe resorts; they're usually contained in one building.
You may book a room in one of these locations when you call to make your reservations. You'll then be charged the extra fee for every night you book, and you're supposed to be guaranteed a room in one of these buildings.
Has anyone ever been assigned to a room in the Allstars "preferred buildings" without having made a reservation there? I'd like to know what they do with the rooms when they don't fill them up with people who have paid for the guaranteed reservations.