I would look into OpenID and Twitter integration (http://apiwiki.twitter.com/Sign-in-with-Twitter http://apiwiki.twitter.com/Sign-in-with-Twitter). But instead

I would look into OpenID and Twitter integration (http://apiwiki.twitter.com/Sign-in-with-Twitter http://apiwiki.twitter.com/Sign-in-with-Twitter). But instead of providing just a text field when accepting OpenID, provide quick links to login with the major, more-general web app providers (Yahoo, Google). You don't even need to tell your users that you're using OpenID for authentication... just that they could login using their existing account with another major web service. You may want to look into RPX (http://rpxnow.com http://rpxnow.com) - it's a commercial provider that does something similar to what I described above. I'm not a huge fan of them being a hosted service, but they do make it really straight-forward to login.