I don't think this is the right solution.
The problem is that certain OpenID providers (most notably, Google, and often Yahoo unless you have set up a named OpenID) use per-domain hashes as their OpenID strings.
This means it is effectively impossible to identify anyone on two different sites using their OpenID, if they choose a provider that uses this same strategy.
We could add 50 different OpenIDs per user, but
- I don't want to force users to have multiple OpenIDs for our convenience.
- Even if you do, you're avoiding the real core problem: what are viable ways to identify the "same" user on two websites, when the user only uses a Google OpenID?
update: we now have a reasonable workaround in place, which is to demand email from Google GMail OpenIDs.
update: I changed my mind and support this due to the proliferation of email addresses, since email = identity. You can now have an unlimited # of credentials (email or URL) associated with your account at the network level.