I found this:
MouseSavers.com - Disney’s Magical Express & Resort Airline Checkin
There is more info on the link, but I pulled this out for ya: (says it was updated 6/1/08?)
Resort Airline Check-in Service
All Disney resort hotel* guests, regardless of whether they are using the Magical Express buses, can get a boarding pass for their return trip home and check in their luggage at their hotel, subject to various restrictions (see below). This luggage check-in and boarding pass service is usually located in the lobby or just outside the front door of the hotel. It is only available for selected airlines (see below).
The Resort Airline Check-in service is operated by a third party company, Baggage Airline Guest Services (BAGS), not by Disney. Essentially the Resort Airline Check-in is like using curbside check-in at the airport, except that you get to do it at the hotel. Plan to tip the baggage handlers who take your bags, just as you would for curbside check-in.
Participating airlines for the resort check-in/boarding pass service are AirTran, Alaska, American, Continental, Delta, JetBlue, Northwest, United/Ted and USAirways.
The Resort Airline Check-In desk daily operating hours are 5:00 am to 1:00 pm, so you really can’t use the resort luggage and check-in service for your return to the airport if your flight departs before about 8:00 am.
As of 6/1/08, you must pay any excess baggage surcharges that apply to your luggage IN ADVANCE:
If you’re flying many of the major airlines, ALL of your checked luggage requires a surcharge.
For some airlines, there is a surcharge only if you have more than one checked bag per person.
To make your advance payment, call BAGS at (407) 284-1231 between 7:00 am and 11:00 pm and pay by MasterCard, Visa or American Express.
The Resort Airline Check-in staff cannot accept any baggage surcharge payments. If you don’t pay the surcharges in advance, you’ll have to check any “excess” bags in at the airport, paying the fees at that time. That means you must take any unpaid bags with you on the Magical Express bus or in your rental car and check them in at the airport counter yourself.
- Only normal-sized bags (generally no more than 62 inches in overall dimensions [length + width + height] and no more than 50 lbs) will be accepted by the Resort Airline Check-in Service. They will NOT accept overweight or oversized luggage – you’ll have to take that to the airport and check it in yourself.
*Resort Airline Check-in Service is available only to guests staying at the official hotels owned and operated by Disney. The Walt Disney World Swan and Dolphin hotels, the seven Downtown Disney hotels and Shades of Green are NOT included.