Between the malware problems and other built-in weaknesses, Windows tends to be associated with a lot of unplanned downtime.
Linux, on the other hand, does not; it's well-known, in fact, for its reliability. Businesses and individuals around the globe would suddenly find themselves getting more done and working more efficiently than ever before. Maybe the GNP would even increase.
4. Worldwide Savings
As companies and individuals the world over stop having to pay exorbitant licensing fees and other software costs, they'd find themselves with surplus cash on their hands as well.
Imagine what could be achieved with the hundreds of dollars per desktop that would be saved as a result--not to mention all the many thousands more from not having to keep up with the hardware upgrade treadmill Windows requires.
5. Better Software
Finally, if everyone were using Linux, the software would just keep getting better, as even more people around the world would be motivated and able to suggest and contribute improvements.
Rather than companies like Microsoft (MSFT) or Apple trying to guess what users want and then delivering it down the road with varying degrees of success, users themselves would have a hand in shaping the software they use and making it what they want.
I certainly don't mean to suggest that Linux is perfect; no operating system is. But given the many tolls Windows takes on its users, the world would clearly be a very different place without it. If everyone used Linux instead, there are many ways in which it would be a better place.
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