In my opinion it is better to compare OpenIDs to credit cards. [...] Just as a credit card company may place limit on the level of guarantee, web sites are at liberty to restrict the OpenIDs it will recognize and accept. Just as many of us carry more than one credit card, we may have multiple OpenIDs and use them for different occasions. Just as some department store credit card is not accepted outside of that store, it is possible that IDs issued by some OpenID providers may not be accepted by some sites.