So you could use credit card numbers, social security number, phone numbers, email addresses, URLs… doesn’t really matter… as long as someone (ideally ONE person) can prove that it’s them coming back to the site.

What you call them or how you publicly refer to them on the site (alias, username, full name, etc) is beyond the scope of OpenID.

To change this is IMHO quite a lot of work. Maybe not so much for us geeks but for mainstream internet. My parents do not have URLs or wouldn’t actually know which one their identification URL is and explaining that to them will be hard. So I really think that trying to somehow e.g. map emails to URIs or that email DNS proposal over at hueniverse might be things to consider.

Of course there is the spam problem and you probably need to have your identifier somewhat public so it makes sense (as I had problems the other day when playing around with some xfn parser/fetcher of mine to actually map my friends profiles together as it wasn’t clear which profile belonged to which identity) and I honestly don’t have a solution for this. But still I see problems of mass adoptions if we don’t go where the people are.

Maybe those identifiers should simply look like email addresses but never be able to receive mail but this defeats my point probably