Just noticed something when i tried to download the WinFx sdk from the Microsoft web site. I was required to validate my windows installation prior to the download. Usually this process is optional but today it was mandatory. After doing some search found out the validation process was made mandatory along with the launch of Windows genuine advantage 1.0
You need to do this process only once and after the first time a key will be stored in your machine for subsequent downloads.
You can also find a FAQ on Windows genuine advantage at http://www.microsoft.com/genuine/downloads/FAQ.aspx?displaylang=en