They call it "Windows Genuine Advantage". The advantage is all Microsoft's, no matter how often and how much they try to tell us they are doing it for our benefit. The system is fatally flawed and Microsoft is in a state of denial over that.
In the last few months, I have seen a 2 year old OEM installation of XP Home (a Compaq laptop) repeatedly be declared invalid. Thank Goodness HPQ is sympathetic and willing to help. Other OEMs have been less receptive and Microsoft's only interest is in getting you to pay for another license, no matter that you already have. They want full retail, too. One has to wonder how many clueless users have paid up in order to not have to deal with the hassles. I'm betting the number is fairly high.
The situation is going to get a whole lot worse when Vista and Longhorn Server get here. Vista will almost completely shut you down if WGA thinks you have a pirated copy or you haven't activated your copy in time. You will be able to use the browser to navigate the Internet, but nothing else. And you get logged off after an hour. False positives here will cause users to shed a LOT of tears, whether of pain or frustration.
Ed Bott's blog on ZDNet has his take on it.
And an older post on WGA.
This is David Berlind's announcement of the kill switch in a
ZDNet blog post.
And in the interest of fairness, Microsoft's justification.
Read it and weep.