I bought a pair of $25 PSN cards two days ago when the gift card deal was first active last week. One of the cards was activated properly, but the second one wasn't. The Target employee properly did whatever activating Target does to the PSN cards, but it turns out Target buys PSN gift cards in bulk from some seller, and they didn't properly activate a batch of cards they sold Target. I found that out when I called Playstation customer service about the card. The customer service rep told me a few people recently called about cards from Target.
The Playstation rep sent me an e-mail, and asked me to reply with photos of my receipt and the front and back of the gift card. He said it would take two days for me to get the credit, and two days later they applied the credit directly to my PSN account.
It was resolved nicely. I still got the credit in time for the flash sale. It's probably not something everyone will have to worry about, but if you do get one of these bum cards Playstation customer service can sort it out. Just be sure to hold on to the card and your receipt.