Here's one for you, Windows vs. Linux: The Patent Tax.

"While $20 might not sound like a lot, it adds up pretty quickly. A school with only 50 Windows machines — barely enough for one class of students — is paying $1,000 of its limited budget in patent tax"

"In the last three years, Microsoft has publicly paid out more than four billion dollars to plaintiffs claiming that Microsoft's Windows and Office products infringed their patents."

and "How does this bill get split up among Microsoft's customers?... [With] 200 million new Windows installations every three years, this means that each of the 200 million new Windows machines is on the hook for over $21.50 in patent taxes."

Ah well, so the figure it likely higher than that because of out of court settlements. Who said taxes couldn't be fun?