Looks pretty legit.
People are saying to use different addresses, you won't and don't need to receive anything via snail-mail, TechNet is all based around your Live account (i.e. Hotmail/MSN). Sign in via that and all of your programs and keys are distributed through the site.
Taken from OCAU from anthony256's thread/post.
http://www.neowin.net/news/software/09/06/03/microsoft-offer…
[Update]: Ars Technica is reporting that this offer may not be for one year as first thought, but only three months. Never-the-less, it's best to get in early and make the most of this while you can.
[Update 2]: It appears as though there are errors in requesting keys and we are hearing that this offer may have been limited to a select few rather than public. Microsoft has not officially responded to requests for comment.
god i hope this isnt dodgy, i signed up.
It asks for a tax id ?? its United States only arrrghhh