I should tell you that I now accept OpenID logins to post comments on this site. You no longer need to create a separate local account here.
For example, if you already have a LiveJournal account, just give your LiveJournal URL in the OpenID box, and it will then go to LiveJournal and authenticate you (you never give your LiveJournal password to my site, of course), and my site will accept LiveJournal’s vouching for your identity.
This helps you limit the number of accounts you have to create and keep track of. It seems to me to be a pretty cool idea.