[JoshTriplett]

I've run into a couple of sites that ask for "nickname" or "preferred form of address", which you could store as a separate opaque string, if you really want that.

[Frondo]

That's great, that's an even better solution. I like that. If I'm ever in a position to make a recommendation about this sort of thing again, I'll use that idea.

[kibwen]

Yes, I'd so much rather have an explicit nickname field if a company wants to insist on calling me anything other than my username.