I was introduced to Free Software in 1996 and I happened to like it a lot, because it was good, and came cheap. The price to performance factor still happens to be one of the important reasons I like it. Very few things are free and priceless at the same time, free software is one of those. And there is a lot more to it. It comes with lots of freedom; freedom to do whatever you want to with it, including making copies of it and distributing it to others, using it for your business or at home, and even selling it. You can learn how it works by looking at the source code, modifying it, fixing problems and sharing the changes etc. There is a certain thrill factor in this whole thing.
I don't have anything against commercial software and would use it if it is affordable, well maintained and supported (and gives me an option to let me or someone on my behalf maintain it if I like it that way). It is also very important that software obeys open standards and gives me a choice between itself and other similar tools without having to lose my existing data. It is unfortunate that these requirements are not satisfied by proprietary software. Free Software often satisfies certain guidelines and a lot of people have access to it and keep improving it.
Richard M. Stallman started the free software movement. There are people who don't like the GNU chant and his insistence that everybody call it as GNU/Linux, and there are many who explain why it is important. RMS's philosophy has made a lot of difference to the software world. O'Reilly publishes a book titled Free as in Freedom on him (free online version). Equally important is the contribution of Linus. Linus showed that there are processes that are not compartmentalized but work really well for software development, delivering what users want.
I follow the happenings in the free software world closely, and I participate on the TwinCLinG mailing list. I was lurking on the BLUG mailing lists for a while, but did not quite like the environment out here. Though the BLUG chaps do useful stuff like foss.in, TwinCLinG suits my taste.
I used to compile and edit The LDP weekly news with Tille. A few years ago, I fixed some design and implementation issues in a file system for the Linux kernel with support for on-the-fly compression. Things move so fast here, that I don't know much about the kernel now. However, I read Linux Weekly News regularly and lurk on the Kernel Newbies mailing list. I would be delighted to do some serious kernel stuff if I get an opportunity again. I am a big fan of the Debian project and contribute there, I applied to be a Debian maintainer and intend to be a Debian developer.
I use free software to develop and maintain this website. There is a page on the details of the software used to create it, and a few reasons why I use it.