Why not log into web sites via email without any password?
jrockway: Because you don't want your sysadmin logging into your favorite dating site as you?If you are going to do this right, you need email encryption.  In which case, you have a client-side certificate.  In which case, you might as well just authenticate over SSL with that certificate.But hey, why do something secure and built-in to every browser (even IE) when you can invent your own protocol instead?  It's the Internet!Also, any reason why this is an "Ask HN" and not a blog post?  (Not saying it should be one or the other... just askin'.)