The Windows XP feature being called WPA "Windows Product Activation" has been getting a huge amount of reaction an scrutiny. (Sounds awful shitty to me). The Ars-Technica guys have gotten the scoop on just what the heck this is all about and if we're actually going to be expected to pay a monthly fee for WindowsXP to be on our machines.

... If WPA is in your copy of Windows XP, you'll have 30 days to activate the product [...] enter your Product ID code at installation, just as before. When contacting Microsoft, you will provide that Product ID code and a "hardware code" generated by WPA. Taking these two numbers, Microsoft will then issue you another ID, and it's this ID that will activate Windows [...] The difference now is that the OS, rather than query a device on COM 2, now queries a central storage system run by Microsoft. If the Product ID is sent off to Microsoft from two different computers, it's going to notice this, and deny the registration. Microsoft's method of discerning one computer from another relies on the Hardware ID generated by the OS.