Passbook is a new iOS 6 feature that replaces all the multitude of wallet apps that store loyalty cards. The eticket feature is also cool, as it gets rid of the need to find the email that has the ticket in it.
It's not clear yet how companies build interfaces to this app, but I imagine there will be information on API's at some point. It doesn't look like people can simply scan their cards. It looks like businesses need to connect their card program to the app.
Apple would have done things a little different from everyone else, so it will be interesting to see how this plays out.
In any case, it is definitely a shot across the bow of companies developing wallet apps.