When Passbook was first demonstrated, I was concerned my carrier of choice, Delta, wouldn't be on board. But lo and behold, the iPhone 5 announcement clearly showed a Delta pass in use. Other vendors hopping on the Passbook wagon appear to be Sheraton and Ticketmaster.
iOS 6 will bring Passbook to supported iOS devices. Passbook is a quick way for users to store their info about vendors -- such as a balance on a Starbucks card -- and a quick way for vendors to check in customers, like Ticketmaster, Sheraton and Delta will be doing.
The original demo in June showed Starbucks, Amtrak, W Hotels and United Airlines along with the Apple Store using Passbook. I can't wait to use it myself.