Last year, the e-mail had an invoice number on it. Mine was 132, so I was #132 to register (and I obviously didn't get to go). I assume this year's will have the same thing...
It will be the same as last year. You will receive an e-mail with your invoice number on it. If it's 105 or below, you have a guaranteed spot. If it's 106 or greater, then you're on the waiting list.