Small transactions will be on the (short term) honour system.
One of the big selling points Bitcoin proponents use to try to get businesses to accept them is that Bitcoins "have no chargebacks." It seems like having every transaction "be on the honor system" is a much, much worse situation than getting virtually-instantaneous confirmation for all transactions upfront and then getting hit with a chargeback every once in a while.
I[n] the days before we had electronic credit card verification the store would take an imprint and only find out later whether the card was good or not.
Yes, and businesses also used to accept personal checks. Have you tried to use one lately? I can't think of any businesses I regularly patronize that accept them today. It used to be that the businesses had to account for bounced checks and declined credit transactions in their business overhead which was ultimately passed on to consumers. By accepting only cash, credit and debit cards with instant electronic verification (my newest credit card doesn't even have the raised lettering for imprint machines since so few transactions use them these days) they can remove this overhead and cut their prices, making them more competitive in the free market.