Dave Kearns recently introduced the work of Danah Boyd to the Identity Gang. I just read through her MIT master’s thesis which has an interesting, and probably sociologically quite valid view on what might constitute "identity" both off-line and on-line. It rings a lot more true to me than much discussion that’s currently going on in "digital identity" circles.
I also very much like her term "face" instead of what we techies usually call "persona".
BTW, if anyone ever wondered why we talk about both "situational software" and "identity" at NetMesh, this thesis provides some very good answers: identity is situational, too, and situational support requires identity. In fact, she uses the term "situation[al]" 71 times in her thesis that’s really about identity…