I used to run Windows. It was already in the pc. It is virtually in any pc, since Microsoft has a share of over 90% of the market (the second player is Apple, which is even more closed), as you can see in the graph and in the table. Why should one bother looking for anything else? When you, as an end user with no particular computer skills, get a pc that works as those of your friends and allows you to do the same stuff, you are ok. That's enough. Windows blue screen of death is something normal if anyone you know had this problem...
If you don't know you have a choice, you can't choose.
Actually, years ago, I did see some Linux distro running on a pc. I had a look and it looked to me so bad and complicated that I didn't even wanted to know more about it. A lot of line commands, something that I did to load games on my old Commodore 64 and on DOS when I was a child. I thought that stuff was outdated. So, was it really a choice for me, a normal person, at that time? No. On the one hand I had the familiar easy windows that all my friends were using, on the other something clearly too complicated for me and in any case just bad looking.
Free as in freedom.
I started downloading programs like Winamp and Firefox simply because I saw some friends using them. Downloading cracked software also was normal. For me names as "free software", "open source", "freeware" etc. just meant gratis stuff. The plus over cracked programs was that they were easier to install since you had no codes, cracks and other issues; and, only secondarily, it was legal.
I didn't care about freedom, simply because I didn't know there was an issue.
Curiosity.
So how did I come close to Linux? Well, after years of downloading stuff, I started getting curious on how to customize Windows. Initially I wanted to have some mac-style eye-candy and other functionalities. I started downloading programs for that and I started reading articles and how to change parameters. Actually I did risky stuff, because I changed registry keys without know what I was doing... But at the end I started learning, more or less, how the system works. In this process I started reading about Linux and free-software.
First approach.
I spent some time reading articles, forums and watching videos about Linux (see my links). And the more I read the more curious I was to try it. Ubuntu seemed the best distro to start with. At the time there was a website offering a simulation of Ubuntu. Also the possibility of trying it live from cd was determinant. And finally I decided to try it...
Bad news.
-First problem. I had no idea about how to make my laptop booting from cd... -Second problem. What installation to choose? Wubi install or partitioning the hd? Wubi seemed easier.
-Third problem. The Wubi install failed. It stopped close to the end. There was nothing to do. The pc was dead and also windows was gone. I didn't have the windows cd. I didn't know what to do. And that was my only pc. Panic.
A new start.
The only solution, before spending money on technical assistance, was to try again with Ubuntu. But now the only thing I could do was a complete install on the entire hd with Ubuntu as my only operative system. It went smoothly. I used Ubuntu as my only system, for work and leisure, for a couple of years. I was forced to learn how to use it. I was forced to find a solution to all the problems I could have. And I learned so many things...
Pros.
It's free. It's gratis. It's stable. No antivirus. No defrag. No formatting. My pc was faster that ever. Amazing and useful graphical effects (I initially thought they were taken from mac, I found out it's just opposite. Btw there are Mac themes like Macbuntu (in Italian), which now is even already packaged into a distro, and Win themes as well). Simplicity in general. Installing applications is much easier and clean. Hardware is generally supported out of the box. Many printers and other stuff are automatically installed when you plug them. Total, really total, customizability. Feel of having the full control on your own machine. Community support. It's legal. New life to old computers.
[Links: 27 buoni motivi per passare a linux - reasons why Linux is better]
Cons.
Some programs are not available for linux. Sometimes the design and the usability of some application is poor compared to similar apps in Win or Mac. Games are mainly developed for win. Too many similar apps, which of course is also good, but when you look for an app you don't want to get lost in too many (and too similar) options. Drivers are not always released for linux, so sometimes the hardware isn't perfectly supported. Watching videos in the internet sometimes can be painful and solving the problem is not immediate (proprietary stuff like flash and silver(moon)light do not always work well and neither their free-software alternatives do). Some distro, like Ubuntu, by default propose you updates of the kernel, which is good if the new kernel is supported by your pc, but otherwise you risk loosing your entire system (and your data): Either you disable kernel updates or you pay attention when times come.
Conclusion.
I suggest anyone to try a GNU/Linux distro. I use Ubuntu and I like it. Try it live from cd (or from usb) without touching your system. You may like it or not, but sure you'll learn something. And that's the important point.
PCs I tried Ubuntu on.
Intel Pentium M 1.50GHz
512MB RAM (then upgraded to 2GB)
Full install, Ubuntu only OS --> This is the first pc I tried. It was ok under WinXP because I kept it clean. When I decided to try Ubuntu, the system crashed and I decided to install Ubuntu as my only OS. I still use it and it works fine. 512MB RAM (then upgraded to 2GB)
Intel Core 2 Duo 2.26GHz
RAM 3GB
Wubi install --> WinXP was slow and the person using it always took viruses. With Ubuntu the pc is faster, stable and safe. And Win is always there, just in case.
Intel Pentium 4 1.60GHz
512MB RAM Initially: Wubi install of Xubuntu. It was fine.
Later: The owner decided for a full install, Ubuntu only OS --> It had WinMe, it was ready for the garbage. Now this pc is still used for simple tasks by different people with no computer skills.
Intel Core Duo 1.66 Ghz
RAM 1GBLiveCD --> Ubuntu seemed to work out of the box (as most of the times). The owner didn't want to try an install and kept WinXP.
Intel Core Duo 1.73 Ghz
RAM 3GB
LiveCD --> Ubuntu seemed to work out of the box (as most of the times). The owner didn't want to try an install and kept WinVista. 
Intel Pentium 4 2.80 GHz
1GB RAM
Full install, Ubuntu only OS --> It had WinXP, very slow and unclean. The owner was going to trash it. With Ubuntu it is reborn. 1GB RAM
Intel Core i7 Q820 1.73GHz
8GB RAM - 500GB 7200rpm
1GB ATI Mobility Radeon HD 4670
HD monitor 1920x1080p WLED
Blu-Ray ROM read and burn
Wubi install --> Win7 is ok, but more demanding and with less effects than Ubuntu. Under Win7 the fan is more noisy. I usually prefer to boot into Ubuntu.
[other more detailed Ubuntu compatibility reports here]
Note on Ubuntu and Free-Software.
Yes, Ubuntu is NOT among the distros Richard Stallman would suggest, because it supports some proprietary software:
Ubuntu provides specific repositories of non-free software, and Canonical expressly promotes and recommends non-free software under the Ubuntu name in some of their distribution channels. Ubuntu offers the option to install only free packages, which means it also offers the option to install non-free packages too. In addition, the version of Linux included in Ubuntu contains firmware blobs.
I understand that, but the point is that people like me arrived to GNU/Linux thanks to the success and usability of Ubuntu ("linux for human beings" they claim). And today once you enter the free-software world, you discover that you actually have a choice. Then you are free to use the software you like, proprietary, free or whatever.
