Comment Yellow Dog -> Ubuntu/Debian -> Arch (Score 1) 867
I started with Yellow Dog on Apple PowerPC hardware, which I mostly used for servers, but played around a bit with various desktop environments. At that time I wasn't doing serious work so much as I just wanted to know as much about various platforms as I could. My primary OS for day-to-day computing was classic Mac OS (System 7, OS 8, OS 9) at that point.
As I moved to x86 hardware and Ubuntu became popular, I used Ubuntu as the primary OS on my development machine at work, and Debian on my servers. Nearly all of my servers (those that don't require anything bleeding-edge) still run Debian stable. Around the same time, I was running Mac OS X as my primary day-to-day OS on my personal machine.
Two or so years ago, I got tired of Ubuntu trying to push a particular desktop "experience" and having multiple layers of indirection and automation to deal with if I wanted to change anything. I briefly passed through Gentoo, which I enjoyed, but found that it required a little bit more time to maintain than was practical for me. I tried Arch and found it to be a good balance between customizability and niceties like binary packages. I switched to Arch on my main desktop at home, still using Mac OS X as my primary on my laptop.
A few months ago, I also switched to Arch on my laptop, more or less removing the Mac from my workflow.