Source Mage is a linux distribution, and a very special one at that. Source Mage is a source based distribution unlike any other. The primary rationale behind Source Mage is to provide the user/system administrator with choice. Source Mage will not make decisions for you, it will ask you what you want.
This paradigm allows you to tailor a system exactly to your own desires. You can create a very light system with only those packages installed that you actually need. There will be no extraneous software installed because some packager felt you needed some specific feature. You are the one who gets to choose the compilation options for all the software you install. You can however also create a complete and fully featured system by enabling each and every feature in sight, ideal when you have a multiuser system shared by many users with greatly varying ideas of what is good software and what are necessary features. Of course Source Mage also provides defaults for all the settings it offers you, these defaults always remain true to the choices of the software developer, we set our defaults to correspond with what you would get if you had compiled and installed the software yourself.
Why I chose Source Mage
I'm a minimalist and a perfectionist, I don't like unnecessary cruft. I use a tiling window manager with minimal window decorations. I use terminal applications and the unix shell as much as I can. For me efficiency, elegance and potency come before flashiness and a shallow learning curve. Aside from that I put great value in customizability of software, everyone is different and everyone has a different way of working and a different way of approaching the world, why would software be any different.
Source Mage fits perfectly in this view. Source Mage allows me to begin with a minimal system and install only that which I deem necessary and only with those features I wish to have. This gives me smaller and faster software with a smaller memory footprint, wich leads to a faster system with less hardware. Source Mage doesn't force hugely complex and large configuration files on me, which I have no hope of ever understanding, let alone modifying to my own content, nor does it force configuration tools on me which change configuration files behind my back. Instead I am given a standard config file that came with the source of the software, which I can easily modify to my own content with the help of the documentation for the software.
Another reason why I like Source Mage is because of my never ending desire to know how and why things work like they do. I take everything apart that I get my hands on and interests me, be it mechanics, electronics or software. Source Mage provides perfectly in this desire because the Source Mage package management suite sorcery is completely implemented in bash scripting. One can easily inspect what a spell (a source package in Source Mage speak) does when you cast (install) it by simply opening the spell files in an editor. If you want to go deeper you can just as easily open the sorcery scripts themselves to find out exactly what happens when you cast a spell, how the spell files are called and what functions are available for use within a spell. Of course this also allows for very easy modification of a spell in the event a spell happens to not offer a certain feature, or the disabling thereof, of the respective software.
Finally there is the welcoming and supportive user community. The #sourcemage IRC channel on freenode is really a wonderful place, there are always people available willing to help out with any problems you might be having with your Source Mage system, or to answer any questions you have. It was really refreshing to find a community actually willing to help new users and draw them into the magical world of Source Mage, instead of the snobbish clubs of elitists one usually finds in community support. Of course the fact that Source Mage attracts a certain audience of like-minded individuals certainly helps here.
My involvement in Source Mage
Not long after I started using Source Mage I started dabbling in writing my own spells for some software which was not yet in the grimoires (Source Mage package collections). I submitted those spells and some updates to a few outdated spells to the Source Mage bugzilla for inclusion in the grimoires and before long I was invited to join the team of Source Mage developers.
My main area of work is the i18n section of the main grimoire, I keep an eye out for bugs in this section on bugzilla and check for new releases of i18n software. Besides that I update and add spells as I encounter them. I can usually be found in the #sourcemage IRC channel on freenode.