What exactly is ruby-build-github, and why should I use it instead of the normal ruby builds?
I came across it while looking into installing Jekyll and using Github Pages.
It makes it easy to install github's fork of ruby (either with rbenv or on its own).
Github's ruby doesn't vary dramatically from "normal" MRI - it's largely backports of things that will be released as part of normal ruby later on.
Github seem to roll out new versions of ruby quite aggressively (according to this [gist]https://gist.github.com/tmm1/8393897) they were running 2.1.0 in production only a fortnight or so after it was released and had run into some of the sharp edges you might expect to encounter.
In general you would have to take a view as to whether you were interested in any of the patches they had applied to mainline ruby, which will of course vary over time