I don't usually preach Linux or BSD systems to the general public for several reasons. The first is that a majority of people I speak to on a daily basis either already use Linux/BSD, so anything I say will be preaching to the choir. And second, a majority of people who do not use it don't because they haven't been trained, and I am lazy and don't really want to train them.
But sometimes I look like "the computer expert" to people who are "newbies," and I am starting to get asked about Linux, or hear comments about it. Here are some of the comments and questions I get, and what I say. I find myself using car/automobile analogies quite often.
"What is Linux?" I say it's an operating system, like Windows is an operating system, but is written not by a company, but a team of thousands of volunteers who write computer code and check each other's work all the time. It's written by people who LOVE computers, and want to keep information about computers public some others can see what's going on. Imagine a world where you buy your car, and get to fool with it to make it run just the way you like. It takes a lot of learning, but there are other mechanics who will happily share with you how to do what you want all the time. Now imagine a world where your car hood is bolted shut, and you have to depend on the person who made the car to fix anything, and you are NOT allowed to find out how the car is made or how it works. The latter is easier for new people who just want to use the car to go somewhere, and don't care how it works, except when it breaks down and costs them a lot of money.
"Should I use Linux?" I don't know. This is usually the hidden question of "What is Linux?" I don't want to say, "Well, how much time do you have to learn it?" because that sounds snobbish. I usually say, "Are you happy with what you have now?" and if they say "Yes," I say, "Then use that." I explain that it's like a trucker's or a motorcycle's license. If you want to learn to use a huge truck or a motorcycle, go ahead. But if you are driving a car, and that's working fine for you, then use the car.
"Linux is a hacker's tool." I could say this is technically correct, but I feel many people who say this mean, "Linux is for those smart computer people who are socially retarded and do illegal things." A hacker, be definition, is someone who breaks apart mechanical things and studies their insides to see how they work. Nothing illegal in that, unless you don't have permission by the thing's owner. A "cracker" is a hacker's term for people who break into things illegally. Like the old word, "safe-cracker." If you live on the streets, though, "cracker" means "white person I don't like," but I digress. I usually ask them to define what they mean, and they get involved in a discussion of some sort. Often people who say that do so out of ignorance, but many are curious, too. We all like crime stories, right? I say, "a hacker is a mechanic who loves to find out how cars work, and tinkers with his own car to make it run better, while a cracker will break into someone else's car and possibly use it for his own crime spree."
"Do you hate Windows?" Not directly. Windows is easier to use, looks nicer, and the games are way better. But I hate Microsoft because of their business practices. They stifle competition, have a product full of security holes, and basically lie, cheat, and steal to get what they want. Microsoft tries to encourage ignorance on behalf of their users to keep them dependant on Microsoft. I like Linux a LOT, but know in my heart it's not perfect. A lot of the Linux GUI managers (KDE/Gnome) need work: they are slow, cumbersome, and have conflicting standards with each build. My main boxes at work and home are Windows 2000 or Windows XP. Windows used to be VERY unstable and crash a lot, but they seem to have fixed most of that. Often I can run them a week at a time before I need to reboot (while before I had to reboot them several times a day). On the other hand, I only have to reboot my Linux boxes when I have to unplug them to move, or at home when a thunderstorm is likely. I have one Linux box at work that has been running over a year and a half without rebooting. Another thing is that Linux will run on older hardware, so you don't have to keep upgrading. When I got Windows XP, I had to buy a new Sound Card, for instance, because it didn't work with XP. My new webcam also did not work with XP, and I don't need it enough to buy a new one, but that pissed me off. The old sound card works great on the Linux box, although the camera doesn't work (this may actually be because I am doing something wrong, and haven't put 100% effort in working on it). I also recognize that Microsoft did set the standards and paved a path for better computing through history, although they sort of forced it because of their "the new Windows needs better hardware to run," which screws the consumer if they don't have disposable money for it. But ye reap what ye sow...
So, as you can see, there are advantages and disadvantages to Windows vs. Linux. Sadly, some people want a more defined answer, like "LINUX r00lz, Windowz sux!" or "Linux is a hacker's tool."