From what I remember from other launches, someone from the Apple store staff will walk down through the line and inquire as to which model/capacity/color you want and how many and state that there is a limit per purchaser, if there is, as well as state if there are any other restrictions such as no cash, credit/debit cards only, etc. In the past they've had restrictions on the number of items per purchaser plus require that purchases be made with a credit/debit card with the purchaser's name on it. This prevents a lot of would-be eBayers from coming into the store with a lot of cash and buying up several or many devices and then reselling them on eBay or Craigslist.