The paid membership comes with 10% off pre-owned games, 10% bonus trade-in credit, and ten issues of @Gamer magazine which has eight coupons for games and accessories in each issue. It's essentially Best Buy's response to GameStop's program.
Also, updated my last post regarding the Best Buy gift cards. If you pre-order at BB, you'll have to wait two or three weeks to get the gift card emailed to you. So keep in mind that you won't be able to turn around and use it for a new game the following week.