Earlier quoted context omitted.
At Google your username appears everywhere. In mail, code reviews, chat, irc - everywhere. I know some of my colleagues by their username only, I don't even remember their real names. When we start we get to specify three usernames in order of preference. You are given the first one that is available. It means a lot to me to be adg@google.com.
do you really want your raw email available publically?
Why are people afraid of having their e-mail address out there without obfuscation?