Okay, so the helmet is definitely fake. A guy called Will on the Engadget thread linked to the picture of the original (440KB); it´s a motorcycle helmet by BMW. He placed it next to the apparent dev kit manual cover in this one and there´s no mistaking.
But don´t despair. There is fresh rumour. The British web design company that had registered the domain nintendoon.co.uk (and who had previously a very simple still on it with no further links) have revamped the site and are showing a cool flash animation on it that looks kind of official. The swf object is titled pre-release. And another intriguing detail: The message in the end reads ´Nintendo ON - comming soon´, obviously insinuating some kind of communications function.