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.
also: I don't know if this was related to the issue introduced by Xcode 6.3, but that recipe for ogre used to fail on my machine. I ended up doing:
wget https://raw.githubusercontent.com/NikolausDemmel/homebrew-simulation/ogre-fixes/ogre1.9.rb
sed -i -e 's/aa9b0c6d371802e0535515758e88c4893045cd5f/45535a9f5a1e462965cf999e222f0b86c3ef679c/g' ogre1.9.rb
brew install ogre1.9.rb --devel
brew install https://raw.githubusercontent.com/NikolausDemmel/homebrew-simulation/ogre-fixes/gazebo2.rb
(but I didn't check if it worked correctly after downgrading to Xcode 6.2)