"This allows consumers the ability to purchase a PS4 at a more affordable price, making it more accessible for gaming fans," said Darron Nielsen, senior merchant of GameStop. We don't fault you for imagining a senior merchant wearing a big, feathery admiral hat.
All "eligible" (so, make sure to call ahead) GameStop stores will stay open November 14 for the console's launch at midnight. Obviously, you'll have to pre-order.
Update: GameStop wanted to clarify Sunday's event further: "The trade in credit will result in the 90% bonus when applied to the PS4 console pre-order. This does not qualify toward the games or accessories. Also, it reads as if customers are able to pre-order at this time, which is not the case. The trade-in offer can be applied to previously pre-ordered consoles."