How many Linux users are there in the world? 5,000? 5,000,000? 50,000,000? No one is really sure. Linux users aren't forced to register their operating system with any corporation; Linux users are free to install and use Linux without anyone ever being the wiser. And what about all of the people who don't even realize they're using Linux? Is Linux running your PDA? Smart Phone? GPS? TiVO? Tablet? Router? Wrist watch? Car? Is Linux lurking inside all of your electronic gadgets? Probably not, but it's turning up more and more these days.