someone could make a program to double spend.  You need huge hash power to make it past a block, but you can broadcast unconfirmed transactions all over the place.  Still, the odds of someone going to the trouble over a few bucks is amost nothing at this point.  Bitpay should offer to cover a loss of a small amount for accepting unconfirmed transactions, and when/if it happens, then make everyone start getting one confirm.  Way too many merchants are demanding tons of confirms and slowing everything down on stuff that no one will ever try to double spend on. Prepaying an hour in advance sounds stupid.  I want to pay like the hot girls in bitpays video:)