Do any of you use sites like Gift Card Granny, Plastic Jungle, or Cardpool to buy discounted gift cards?

I'm considering ordering some for places we regularly shop at: Petco, Target, etc. as a way to save money on the basics.

Essentially, the sites off a gift card at a discount. You can then use it at the store or online to make regular purchases and still use promo codes, etc. since this is just a form of payment.

Just wanted to know if anyone had any positive/negative reviews?

I'm thinking if I combine a discount gift card, ebates, and promo codes, I could save quite a bit on my pet food which is one thing that is $$$$$.