In an amazing synchronised presentation at OSCON 2005 (in a style attributed to Lessig) Dick Hardt spoke about digital identity.
In this 15 minute video Hardt speaks about authenticating and
managing real-world identities online.
Download it even if it is just to see the presentation style and an effective use of Powerpoint.
For a discussion of the legal issues relating to on-line identities, read Kim Cameron’s The Laws of Identity.