Wired has an article on successful tech entrepreneur Doug Humphrey, wherein he discusses his decision to move his company to all Macs. He has an excellent quote:

"We avoid the Windows operating system since it is such a huge security risk," he explained. "We didn't want to have viruses blowing up systems that we depend on for navigation and monitoring engines and other systems. And since nothing seems to be able to stop all of these Windows viruses, the best way to win is to just stop using Windows." (emphasis added)