Flights are one of the very few areas I have found QR codes to be useful. I'm usually able to check-in on my phone during the drive to the airport, add it to Passbook, and by the time I'm at the TSA screening area the ticket has made it's way to my watch. I'm always a little wary of clunking my watch on the glass screen of the barcode reader, but haven't had a problem yet.

One time, on an American flight, the scanner at the gate was somewhat of a C shape and my watch + wrist wasn't able to fit inside of it, which was quickly resolved by pulling out my phone and sliding it into the scanner.

On another positive note, TSA agents love it and always accuse me of being James Bond. Makes the screening process much more fun.