The OpenID concept is a good one, and the questions about true identity are valid. However, the 'special features' or services that Dot Gov sites would provide would NOT be those used for actual business, but rather for the kind of information or collaboration that are not necessarily full access. As an example, my bank or brokerage might allow me some specialized features like research or social collab features with only an OpenID account, as a convenience for not registering with the site to get these faetures, BUT would require fully authenticated account registration for doing business. The Dot Gov sites would do the same.
Information gathering or forum participation might only need my Farnham identifier, but serious stuff like my taxes or social security information would need Barry's real information, and both parties need assurance that we are who we say we are. Multi-level communications in the digital arena is a useful state of operation, but needs user education.