If I understand correctly, using OpenID means that Site A can confirm that User X is the same as User X on Site B, using OpenID?
I can see where that's a win for sites A & B. I can also see many instances where that is not a win for me.
Everything gets forwarded to the same inbox.
tuffmail.com is awesome and cheap; I'm a happy subscriber.
Of course, in reality, both sites will request your email address, so they can figure it out anyway.
Between this and your comments on G+, you seem really interested in villianizing your service providers when there are obvious ways to avoid their naive account associations [1], as you even take advantage of.
[1] I say naive because I would be willing to be a large amount of money that I could track you between accounts unless you're taking some insane precautions against it, even without an email address or OpenID url.
For casual purposes, which encompasses much of my present threat model, the measures I'm taking should be reasonably sufficient.
The point I and others are making is that:
0. There's a growing default assumption that individuals have no privacy, that privacy is dead, and that we should all just roll over and forget about it.
1. Even if you trust your service provider today, you may not trust them tomorrow.
2. Even if you trust your service provider, you may not trust those who have access to your data through your service provider. Intentionally or otherwise.
I'm well aware that roughly 32 bits of leaked information should be sufficient to identify me, if not precisely, then with reasonable accuracy. This doesn't mean I'm going to hand over my SSN and DOB to anyone who asks.
It may also be the case that I'm deliberately trying to create various associated identities.
That said: if you're interested in trying to link this identity to others, you can GMail me any of your prospective linkings.