I see two problems: whenever the system goes down, the park stops making money... even if it's only for a little while (every time something was down for a "little while" at KI it was always like 30min...) it might make people decide that they don't need to get that drink anyway, so the park will lose revenue on that. Also, since their main marketing push is "you won't lose your cash", what if you lose the card...? Oh, and if you don't spend all the money on it, can you get a refund for the remaining balance? I see no problem with this if it's an option, but it's stupid to require it.