Yesterday, word came down from Microsoft that nearly a quarter of all Windows installs world-wide were classified as "non-genuine" by the Windows Genuine Advantage tool which checks license validity. Since it's launch in 2005, the system has attempted to validate 512 million users, and tagged 22.3% as invalid. That's 114,176,000 pirated copies out there in the wild according to Microsoft's statistics.
The WGA program has come under heavy fire due to the system mislabling valid installs as invalid and causing a great deal of customer headaches when upgrading hardware. There is no indication of how many of the 22.3% might be false-positives.
WGA is more deeply entrenched with the upcoming Windows Vista and Office 2007 products.