This is really great. There's quite a few places where I'd love to sign-in like this. The one area where I think it would fall down is logging into web apps th

This is really great. There's quite a few places where I'd love to sign-in like this. The one area where I think it would fall down is logging into web apps that have multiple points-of-entry. Such as chartbeat(phone app and website). I don't see how you would be sent a link to log into an iPhone app. Or could you be sent and email with multiple links: one that goes to the site, another that flings you into an app? The best implementation would be if web apps offered this in the preferences area with a check-box saying: "Enable NoPassword" (so you don't offend any traditional password lovers or confuse people that just might not understand it).