These instructions have been supplanted by an automated, scripted installer, which lives here:
https://github.com/mikepurvis/ros-install-osx
Please try it out, and file bugs as required. Feel free to browse past versions of this gist as a historical curiosity, but I won't be monitoring or supporting it any more.
Thanks for the recipe.
It seems like the location of brew recently changed to
ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"