When I created my account on bugzilla, my question was : why give email as a username ?
That's for good reasons, mostly that people can more easily remember their email address than some random username, and it's guaranteed to be unique. All the web apps I produce/produced use that technique.
It does mean that for public services you have to be careful about exposing the email address in public of course though. That shouldn't be hard to add to bugzilla.