Vagrant
I love the notion of a clean, repeatable install. In my side projects, I've historically accomplished this through strict documentation practices and directory organization. However, this process inevitably breaks down for me when a machine becomes multi-purpose.
Either locally or in the cloud, I'll end up installing packages, hacking together configuration, or otherwise making the environment murky. In fact, the server that currently hosts this blog is a perfect example. This instance hosts this site, riiga.net, and has been a sandbox for toy projects I've worked on over the past two years.
While I'm reasonably confident I can redeploy this machine within a couple of hours, it would be far …continue.