Why should I use OpenID?
simonw: OpenID is not a replacement for your users table. The first time someone logs in with an OpenID you haven't seen before, there's nothing to stop you from asking them for their e-mail address (you can even send them a challenge e-mail if you want to be sure). All OpenID really does is provides your users with an alternative to setting up Yet Another username and password just for your site. It also lets people opt-in to correlate their accounts across multiple services, which is useful for both you and for them.If OpenID meant giving up the user database (the crown jewels of any site) it wouldn't have a chance of being adopted by anyone.