I've got two pieces of advice to add to the conversation, and admit up front that they may seem counter-intuitive to one-another.
First, don't just jump in and buy a PAP. Consider how often you use the Water Parks or Disney Quest.
DVC Members get a discount on Water Park and DQ single-day tickets. The discounted price is $48.19 (adult) / $40.67 (child) for water parks, and $41.22 (adult) / $35.47 (child) for DQ. The difference between the AP and PAP is $105 (adult) / $97 (child). This means you need to visit the Water Parks/DisneyQuest at least 3 times during the course of the ticket for the PAP to pay for itself.
But wait, don't stop the comparison there. Maybe one person in your group should still get the PAP even if you won't go to the Water Parks/DisneyQuest that many times.
The Premium Annual Pass gets a 20% discount on purchases as compared to the 10% on the regular Annual Pass. (Note, the passholder discounts are only on merchandise, and not on food.) Even if you never visit a Water Park/DisneyQuest, but spend more than $1,050.00 in merchandise over the life of a pass, it may still be worth it for one person in your family to get a PAP instead of an AP. (Hey, if you're using the pass for two-years worth of trips, that's $525 per year. Believe me, it's not an unreachable amount.) If you're doing a combo -- some water park days and some merchandise -- figure out your own breakeven point and determine if a PAP for at least one person makes sense.
The down side of having a PAP for a single person in your family is that this person has to be the one to pay for all merchandise. (Believe me, they're strict. You not only have to show your PAP and photo ID for the 20%, but the name on the PAP needs to match the payment card.) I was that guy on a recent trip, so I never had the option to say, "No, I don't feel up to going to Downtown Disney, tonight. You guys go ahead without me."