Chances are the only ones who will try this are your users already using two-factor auth somewhere else, and it's most likely they got started with Google. Migh

Chances are the only ones who will try this are your users already using two-factor auth somewhere else, and it's most likely they got started with Google. Might as well use an app that's already on their phones, Google Authenticator (http://news.ycombinator.com/item?id=4348475 http://news.ycombinator.com/item?id=4348475)