I just joined too. I'll be getting Park Hopper passes, and the discount on those is 5%. After buying 4 five-day hoppers, the DC card will have more than paid for itself. I got the card for only $29.95, thanks to a discount code I saw on mousesavers.com.
Hoping to also get other good savings out of the card too. It was neat to read how some of the rest of you have saved because of having the DC membership.