The QSDP in 2012 is ~$35 per night per adult. On it you get 2 QS meals and 1snack per person per night, plus the mug. QSDP, especially in 2012, has the thinnest margin of them all, making it a bit more difficult to save money on it.
This $35 per night translates into about $16 per CS meal (using an average $3 snack) just to break even. If you think you (as a party) will easily hit that mark with entree, drink, dessert (yes, you get dessert @ CS meals) then it's likely a good idea. If you don't think you will, or are uninterested in parts of the plan (skip dessert, drink water, etc), then it's probably best that you skip the plan and just pay OOP. To get that "pre-pay" feel, pick up a gift card or two for the cost of the plan and pay with that (ideally, charge to the room and pay that charge off with the GC, it's easier).
Also as a note, if you are still undecided you can go ahead and book anyway. Up until 45 days out, there is no fee for changing your reservation. After 45 days, there is a nominal fee charged for changes that's often waived if the package is increasing in price. Starting about a week out there is a steeper fee (~$50) for changes that is rarely waived either way. You must decide to add/remove/modify a dining plan by at the very least 72 hours out. After that mark, you're locked in.