Windows Genuine Advantage suffers worldwide outage, problems galore
Source: http://arstechnica.com/news.ars/post/20070825-windows-genuine-advantage-suffers-worldwide-outage-problems-galore.html
For those of you doing installations and upgrades this weekend, we recommend that you avoid activation at this time. Remember that you can run Windows legally for 30 days without activating.
If you attempt a validation and it fails, your install may be marked as non-genuine, which could lead to several annoyances. First things first, do not reboot a Windows machine that has been marked as non-genuine. Once you do so, you will lose functionality and the Aero interface. It would be best to wait until this problem has been resolved.