Look, here's the deal with Game Crazy and all other cards:
If you spend a lot of money on used games, all the cards are going to work to your advantage. I could be wrong, but I'm guessing that the point of the cards is to get you in their store. If you have an EB card, their logic is "why would they go to Gamestop when they can save 10% here?".
I know a guy who has bought more than $3,000 worth of games at Gamestop over the last year. He saved $290 and I laugh in Gamestop's face if they think they ripped him off becasue he would have spent that money there anyway.
The problem with Game Crazy:
1) They charge double the already-established $10 rate of Gamestop and EB's cards
2) You get no free magazine subscription
3) They preach their "bonus offers" like gospel - the ones that change every month. Granted, sometimes they have really good deals, but other times their deals are crap. This past month you get a free hat with pre-order if you have MVP? Look, we are all somewhere on the nerd scale here just being a part of this thread, but can anybody here honestly say they can imagine any situation other than Halloween when you would WANT to be seen in public wearing a Game Crazy hat? Even though they "promise" great deals in the future, it makes you feel like you're being taken.
4) They post their January deals in the middle of January "All month long, games are XYZ% off", February deals in the middle of February, and here we are on March 6 arguing about what the March deal is "going to be". They don't have their crap together and if they're going to sell you a bonus card under the auspices of having monthly deals, then the Feb deal needs to start when the Jan deal ends and so on. I do not feel that they keep up their half of the bargain.
Those are my problems with Game Crazy. You can't just buy a card and say "this is what I have". You have to play their little game all the time. And in the end they determine whether you have something of any value from month to month or whether they're going to use their card as a vehicle to get rid of their extra crap.
Even still, if you spend enough money on used games and if you are foolish enough to trade in your games at a game store, just do the math and be thankful for the fact that the numbers fall in your favor.