I thought this entry over at HackWire was kinda funny, usually with these kinds of contests the winning information is a little more hidden(flip side of cap insert)

Who is more mad, Pepsi, the consumers who can't ever win or Apple? Posted on MacMerc is the secret to always finding the winning caps with the free iTunes song codes printed in them. No need to crack the code, or use the x-ray goggles, simply tilt the bottle at a 25 degree angle and view inside, if you see random numbers your a winner, if you see 'again' its short for 'try again'. The article has great pictures of the exploit in action.