Well, this is what you get when copy protection runs amok. When you think more about making sure that your customers can't copy your software than you do about the customer's needs.
If you use Windows, do your best to avoid anything that requires a ping to WGA. That means you should stay away from patches and add-ons until the coast is clear. WGA will not reach out across the Internet and deactivate your copy of Windows, but you should avoid talking to a WGA server for any reason.
Now, while you can run Vista unvalidated for 30 days, this is just ridiculous. Thanks to just a couple mistakes on Micro$oft's part there are huge amounts of 100% legit copies getting invalidated. When this happens you can't apply patches, and you lose Vista's one nifty feature, the Aero interface.
So, all thanks to copy protection... you can't use your own copy of Vista. What more, pirates simply disable WGA on their copies of Vista, so they're perfectly unaffected by this. That's right! You, the paying customer, got screwed while the pirates are just laughing at you.
A prediction: When the server comes back up on Monday, and everyone in the world tries to revalidate at the same time, the WGA server may very well be unable to handle the influx and go down again.
Update:
Customers who received an incorrect validation response can fix their system by revalidating on our site (http://www.microsoft.com/genuine). We encourage anyone who received a validation failure since Friday evening to do this now. After successfully revalidating any affected system should be rebooted to ensure the genuine-only features are restored.
Guess they thought it would be a bad move to leave people stranded for three days without the only thing that makes Vista seem okay, the Aero interface. Even then, it's stupid that this should ever happen in the first place. When you buy something you shouldn't have to worry about your legit $400 copy of Windows Vista suddenly stopping working, just because the company is trying to stop a little piracy!
Personally, I hope this turns off at least a few people to Microsoft, and their DRM obsession.