Earlier quoted context omitted.
I always thought that the problem with openID is they didn't use email addresses instead of URLs. e.g. use john@example.com and require a certain url template for the endpoint e.g. example.com/openid/john That way I don't have to remember another identifier and we already trust at least part of our identity to our email provider. Not perhaps as open, but much more approachable as a user.
Hate that idea. I don't want to have to share my email address, in fact that's a primary reason why I always use my open ID (which is unrelated) when possible. Providing email as a credential creates an implicit, if not explicit, invitation "Here, spam me." This is why I'm generally against using email as an identifier. Other examples that all suck for this reason: Apple IDs. Windows Live ID. Jabber.
Erm, to clarify, Jabber isn't an authentication system. It's a decentralized IM network, structured similarly to email. A user is identified by their username on a given host, just like email. It (sensibly, in my opinion) re-uses the same format for that, user@host (I don't think user!host would be quite as intuitive...).
This does not mean a Jabber ID is an email address. It can be, but they are two distinct properties of any given identifier. So saying it 'sucks' because of the format of its identifiers happens to look like an email address, and some services choose to enable both email and IM on the same ID, is stretching it a bit.