Check out Fork the Cookbook[0], which uses such a thing. The main complaint (about 10 each week) is that people expect to have only one password. It's not really as user friendly as you think
Fork the Cookbook emails the user a password, but that's not what I'm suggesting. What I'm suggesting is completely password-less: You receive a link like http://example.com/log-in/0039392030202 in your email and just click that to log in and stay logged in for e.g. two months.
The link expires within an hour, and once logged in you're logged in for a day.
People complain about that shit every week. We switched to Persona for a week. Even worse results. The only reason why I'm keeping this for FtC is because I don't want to deal with passwords and hashing and stuff.