In many human societies we use two names: an individual identifier and a clan identifier. Sometimes the clan identifier is on its devolutionary way to a simple disambiguator, but even so a name like "Chen" immediately differentiates one from another named "Sigridsdottir". And so it is on the net: two people with the same username at world.std.com and radix.net are (probably) just two different people, but the first is probably from New England and the second from DC.
Lately I have identified more with TCNE (my rally club) and less with Arisia or Harvard. And thus I've stopped giving out addresses @arisia.org (which I'm not sure even works any more) or @post.harvard.edu (which does) started giving out my tcne.net address from time to time, and more rarely sending mail with that for a return address. But even though I was inching away from it, the loss of that account is a blow to my identity.
It's all well to talk of growing up and moving on, and there are certainly aspects of my time at the Ranch which it will be good to leave a little further behind. But let's acknowledge what is being lost along the way.