The double xp site is up, and you enter the codes on the site after you register with Pepsi...( I registered years ago for free iTunes, and forgot all about it, so it was easy for me.) After you enter your codes, they have a button to link to your GT, simple as well.
I drink a TON of DEW, but not 12 pack cans or 20 oz bottles, so I really didn't have very many codes. (12 pack cans yield 6 codes, in the inside of the cardboard case...20 oz bottles/orange cap=one code good for your next 3 matches.) I used 2 codes from the 20 oz, and never could tell if I got my xp...There doesn't seem to be anything that denotes it on LIVE while playing. I have a buddy that is using a bunch of them, and he said the other night that he was out of double xp, and needed to enter more codes...not sure how he knew, unless he was counting the matches.
"Once you learn good English...Can't nobody take it away!"
Xbox LIVE Gamertag: KEVIN G 40