And you have to carry your phone around too. And I suspect phones will eventually become the default proof that you are you, phones being more personal than personal computers have proved to be.

But a USB dongle could save you from having to log in at all, which is the ideal. You visit a site and it knows you are you, (it looking for and finding your dongle), avoiding your: "I click on the 'Log In' button, select the email address I want to use, and _that's it_." And as to your phone, it should be able to imitate being a dongle.