(A companion page to why I use Linux.)
In a nutshell: It's legally free (both the operating system and a plethora of software, providing you can get your hands on a copy without spending money—though even if you can't get it free, you can get it damn cheaply). It's safer, and more reliable than Windows. And instead of unexplained crashes, like Windows does, you get proper error reports that allow you to properly debug a system. Not to mention that it's a proper multi-user system—where each user is prevented from mucking up other users files and settings, and prevented from mucking up system files and settings.
But I won't deny that Linux is best suited for being used as a real computer by people who're interested in computing. i.e. If you want to play games, buy something that's designed for that role: A games console, not a Windows PC (unless you like wasting a lot of your time and money maintaining it). Windows is best suited to young teenage boys who break things, like pulling things to bits to try and guess at how they work (though frequently not accomplishing that), and don't mind putting up with broken toys. If you want a computer, as a computer, and don't want to know how it works, then get a Macintosh—they're designed to be used and not fiddled with.
For someone who wants to type, e-mail, browse the world wide web, and do all the things that involve communication using a computer, Linux is well suited to the task. It's more than capable of it, and most of those services are actually run on some Unix-derivitive anyway (Linux is based on the concepts of Unix—a professional computer operating system with forty-odd years of history). And it's going to do what you want it to, not what some malcontent kid on the internet wants to do to your PC. So you're not having to fork out protection money to anti-virus, anti-trojan, anti-spyware, and firewall vendors. Most of the dross on the internet is aimed at knobbling Windows, Linux works in an entirely different fashion. It's not immune, nothing is; but it's less of a target, and one that's much harder to hit.
So what do you get with it? As well as the operating system, you usually get at least three different programs that do the following kinds of tasks:
And many other things…
There's 658 packages installed on one of my systems, and I've only installed just some of what's available. Granted that some of them are multiple parts to one thing that works as a system, but it goes to show that it comes with quite a lot of things to start with (three CD-ROMs worth).
What do you get with Windows? An expensive operating system with annoying and unfathomable license encumberances, wimp-out disclaimers, and you still need to buy separate expensive software that's just as burdensome. Not to mention having to pay for licenses for other computers to interact with your server. And you have to spend more of your money trying to fix it up. Microsoft is the shonky car dealer of the computing industry.
What do I get from Linux? A system that runs non-stop for at least a month without crashing. It doesn't wipe out files and blame me for it (like Windows and the usual stern “you didn't shut down properly warning” you get when it tries to boot up after it crashed while you were properly closing down the system, or were in the middle of actually using it). And if a Linux application does crash, it's rare that it stuffs up other things at the same time—the crashed program just dies off. You, also, get a complete system that keeps itself up-to-date in a simple manner (both the operating system and application software), and it comes with drivers for all the hardware that it supports.
If you can learn all the wierd things that Windows expects you to do, to be able to use it, then you can certainly manage to learn how a proper computer system works. Give it a go, even if you're only slightly curious.