Version upgrading becomes a continuous plain for developers. Plugins, packages, frameworks, languages and now Mac OS come to offer an upgrade. If you wait until your current one goes deprecated or unsupported, you may be likely to spend a few times more hours on it. Besides, various dependencies will make any upgrading risky. Fortunately, Mountain Lion seems not to get things too messy, but majorly you have to install Xcode 4.4 and reinstall imagmagick and Rmagick if they are used. Only a few steps to go on Mountain Lion:

1. Install Xcode 4.4 from App Store

2. Install Commands Line Tools from Xcode, Preference -> Downloads

3. Install XQuartz

4. In terminal:

1
2
3

  brew update
  brew unlink imagmagick
  brew install --fresh imagemagick

It takes a few mintues, but can’t be simpler to go.