I know you were joking, but that's kind of an interesting idea, using e-mail as a login solution. To log in to Hacker News for example, you would type your e-mail address on HN and in response get an email with your session link in it. With a good enough e-mail reader it might not be as painful as it sounds, and it would eliminate passwords and there would be no difference between registering for a site and logging in to a site.