Arch Linux
Arch Linux is a distribution I've peeked at once in a while, but never really touched it, until Lennart installed it on his Raspberry PI. I followed, I liked. I quickly wrote about it: Raspberry PI, installing Arch Linux on USB drive
I even did a video: Hipster introduction to Arch Linux.
Now, I've installed it on my main work laptop and to be honest, I'm still banging my head into the things that are different from the debian and ubuntu world.
Why I went from Ubuntu to Arch Linux
I love learning new things and I love the concept of the package manager fetching sources and a much more agile and progressive package management, where you're not stuck with a version of $program until the next major release. This maybe is great for production servers, but continuous upstream is really nice.My main machine for programming is not the most powerful, so I actually benefit from Arch being a leaner distro, even though I'm running it with Gnome 3.
Since my most commonly used applications are browser, mail client, terminal and vim, there's not a lot that I have to worry about, when switching distributions. Maybe I'll do some smaller posts in the future that target a couple of the pitfalls when you, like me, want to run Arch and come from the Ubuntu/Debian World.