An OpenID identity is just a URL. You can have multiple identities in the same way you can have multiple URLs. All OpenID does is provide a way to prove that you own a URL (identity). And it does this without passing around your password, your email address, or anything you don't want it to. There's no profile exchange component at all: your profiile is your identity URL, but recipients of your identity can then learn more about you from any public, semantically interesting documents linked thereunder (FOAF, RSS, Atom, vCARD, etc.).
Just discovered that stuff developped by Danga. Not sure I understand exactly how it's supposed to work.