This is a neat idea by Second Gear: instead of the regular newsletter, they’ll be using Passbook to gradually release information about their new app.
In Italy, I’ve seen a couple of services that are starting to use Passbook. Pit Pass is the first item that I’ve added to my Passbook since its launch last year, and I’m intrigued by the prospect of more developers using it to tease upcoming apps.
Lex Friedman has a nice overview of Pit Pass at Macworld. As an aside, I’ve also found out today that Passbook files can be viewed in Mountain Lion’s Mail through a popover.