They are more than likely to be clicking a link in the email anyway, so why not remove the barrier to entry (password). OKCupid emails have a big "call to actio

They are more than likely to be clicking a link in the email anyway, so why not remove the barrier to entry (password). OKCupid emails have a big "call to action" button that says "Login instantly" (or something similar), you click it, you log in. Simples :)