Currently for CMs they are doing a special until 6/3 (I think) and you get 60% off (if you ar in the room) and 50% off (friends and family-if you aren't staying in the room) plus the
DDP for $25.99.
My brother and I went in March (I'm a Seasonal CM) and we got 60% off and the discount ddp and it was very nice! In March we had the choice to get the QS DDP or the DDP but for the current promotion, it's just the regular DDP.
You have to call WDW CAST to book any package that includes the DDP and you can't always get the DDP if you book a friends/family room, although from Jan - June 2010 you are able to add the DDP for a friends/family room.
You can't just add the DDP to a Cast reservation unless they are offering a special with it since usually you have to get the DDP with a package including tickets.
When you are signed onto the HUB, you can just check WDW Resort Discounts and right on that page will give you a link as to if the DDP is offered and for what length of time.
If not, they will always offer at least 50% for you, 40% friends and family, and 30%-if the other 2 are booked already--off room only reservations. For busy holiday times, book early, there have been times where I had a hard time getting a resort reservation for a certain category-Value, Moderate, Deluxe, Villa.