There are several other things you may want to know about room discounted bounceback offers. (Bounceback can mean either a discount on room only prices or a discount or free standard dining packages. I can't address the dining package.)
If it is offered, you'll have to book within a specific set of dates: As posted in December 2007, the 2008 bounceback dates were:
1/6 to 2/2/08
2/24 to 3/1/08
3/30 to 4/12/08
8/10 to 9/27/08
These dates applied to deluxe resorts. If rooms were available, you could book a room and receive 30 percent off the regular rate for these dates. (Deluxe Villa dates were roughly the same dates but the offer for them was 40% off.)
Information from other websites has reported the specific dates as:
Value resorts, 20% off most nights 3/30/08-4/21/08; 8/10/08-9/27/08; 10/19/08-11/1/08; 11/9/08-11/15/08; 11/30/08-12/13/08.
Moderate resorts, 30% off most nights 3/30/08-4/21/08; 8/10/08-9/27/08; 10/19/08-11/1/08; 11/9/08-11/15/08; 11/30/08-12/13/08.
Deluxe resorts, 30% off most nights 3/30/08-4/21/08; 8/10/08-9/27/08; 10/19/08-11/1/08; 11/9/08-11/15/08; 11/30/08-12/13/08.
DVC/Deluxe Villa resorts, 40% off most nights 3/30/08-4/21/08; 8/10/08-9/27/08; 10/19/08-11/1/08; 11/9/08-11/15/08; 11/30/08-12/13/08.
The instructions say you must book before you checkout. Plan on spending a while on the phone in your resort. (I spent 45 minutes on the phone.) Modifications can be made (subject to availability) after you return home. You simply need to make the standard deposit for a room only reservation (but note there is some dispute about whether the cancellation period is now 6 days or 46 days before the stay).
Finally, some people learn about bounceback offers through flyers in the room, on the tv channel or by asking. Even if you don't see any mention of it, ask about it at the front desk.