Well apparently a lot of people are having WGA issues:
Microsoft's WGA servers are currently flagging genuine installations of Vista as counterfeit and disabling Aero and other functionality as well as a punishment. You will encounter this if you try to download any files from Microsoft's download site that require that validation to download, for example, DirectX updates. No news from Microsoft as to when they will fix the problem. Most annoying, to say the least!
Now this isn't official so...
Man, what a yucky feeling to be flagged like that. Where is my Ubuntu DVD...
There is a techmeme thread here.
From the Arstechnica article:
Microsoft is telling users who are affected that they should "try again" later, with some support techs telling readers that Microsoft is aiming to have a fix in place by Tuesday, August 28th. That would mean the outage will last more than three days, given that it started last night (and may have started earlier, we're hearing reports of some users running into this earlier in the week, on limited bases).
Looks like the problem is fixed.