I posed the same question on here and the Blowout forum. I got 12 responses from each place.
My fellow bloggers reported a total of 13 cards unlocked for 169 codes entered. This includes bonus codes. That's a paltry 7.69% of codes that get you anything you can hold in your hand. That number is skewed a bit by the fact that 2 of the 12 people got 8 of the cards. Six people got zilch.
The Blowout folks reported a total of 39 real cards unlocked by the whopping 834 codes entered. One guy alone got 10 cards for his 300 codes. The Blowout percentage is even worse than ours as it is only 4.68%.
I'm hoping to get a few more replies to yesterday's question. Feel free to go back and answer it. I'd give you a link but I'm typing this on my phone while I eat my Cheerios.