"Open source legal services firm Software Freedom Law Centre has
calculated that Microsoft Windows users pay in the region of $20
per operating system installation to account for patent
infringement claims against the software giant.
"The 'patent tax,' as SFLC called it, is based on the amount of
money Microsoft has spent on settling patent infringement claims
involving Windows and Office over the last three years as well as
legal fees during the same period, divided by the estimated number
of Windows installations..."