Who's hip to it:
· Air Canada *new this month
· American Airlines
· ANA *domestic flights only
· Malaysian Airlines
· Porter Airlines
· Qantas *new this month
· Turkish Airlines *new this month
· Virgin Australia
Coming soon: British Airways and Delta. According to TUAW, British Airways are looking to add Passbook "as soon as [they] can." Delta, on the other hand, despite being featured in the Apple keynote regarding Passbook, still hasn't managed to push out their Passbook compatibility. The last Delta app update came in June 2012.
In order to add an upcoming flight on one of the above airlines to your Passbook, make sure you're running iOS 6. Login to your account on the airline's app or, for a few, there's a link on your emailed flight confirmation that lets you automatically send it to Passbook.
[Images: the respective airlines]