The Security Mentor

The name is confusing enough, the actual workings are murky, the accusations are hard to judge, but Windows advocate Paul Thurrott has a short and readable recap of what WGA does and what it's supposed to do.
UPDATE 8/18/2006:
It turns out that WGA was working exactly the way it's supposed to: Paul Thurrott had, in good faith, bought a copy of Windows from a shop that was pirating them. His apparent problems came from WGA detecting that the copy he'd paid for was actually unauthorized.