I just came across https://www.grc.com/sqrl/sqrl.htm

With Secure QR Login, your phone snaps the QR code displayed on a website's login page . . . . and YOU are securely logged in.

This seems like it would be pretty awesome - one of the problems that I can think of is if the QR reader is compromised, to display www.google.com instead of www.nsa-super-secret-place.gov/123. What other problems does this system have?