I'm a part of their gamer zone program. You have to have "unlimited" unlock or something, which is $14.99 a year. I think its worth it, I pre ordered Borderlands 2 and got my $20 certificate last week. Next game I got pre ordered is Black ops 2. You get points for every purchase and you get $5 back every 250 points.
The $20 is a best buy thing, you still get regular pre orders too like Blops2's nuketown. Hope this helps.