Supposedly, billg@microsoft.com is the e-mail address of Bill Gates.
Addresses within Microsoft are set up like FirstNameLastInitial@microsoft.com, (i.e. Jimbo Smith would be jimbos@microsoft.com). From this, Bill Gates would get the login billg. On the other hand, there are probably enough Bill Gordons, Bill Grays, Bill Grahams, etc. that billg could go to a person besides Mr. Gates. But, Bill Gates has priority, being president and all, so it is possible billg is he.
Chances are that if this account does belong to Bill Gates he doesn't read the account directly. He probably has armies of secretaries screening his mail, (or a really good filter program). After all, what good is a mailbox full of messages like:
BILL GATES Y00 suck! My Windows ME crashed fifteen times when I was playing Tribes 2 yesterday and I hope you die and all your money goes to charity to feed children in india you creep. Johnny Haxx0r.
But once in a while a message is actually replied to. Usually the reply is very short - just a few words. A slashdotter claimed that his question on whether there was truth to a rumour regarding Windows supporting a certain exotic video card produced the reply:
no truth
And once in a while, a random WINDOWS SUCKS message garners this response:
why?
Is it really William Gates III, or just another MS programmer having a laugh? We may never know.