I have my winner; my problem is I'm not sure what to do.
I thought I'd closed every loophole, not having done this before. But I have a bunch of emails with a screen shot of 1000000 on it, and I trust the senders to be honest.
So obviously there's some oddness about the counter, or about browsers, or something.
Given that I did say several times that I would be giving away one copy to one entrant, I am thinking that no one would expect me to do other than send that copy to the first person to email me a 1000000th visitor screenshot.
UPDATE: the winner's name is Ben Thompson. Congratulations, Ben!