As you can see below, libv8 installs fine, but therubyracer doesn\'t. I\'m using Mac 10.7.4.
~/.rvm/rubies/ruby-1.9.3-p125/lib/ruby/1.9.1> gem install lib
@Haegin's answer in https://github.com/cowboyd/libv8/issues/205
brew uninstall v8 brew install v8-315 gem uninstall -a libv8 gem uninstall -a therubyracer gem install libv8 -v '3.16.14.17' -- --with-system-v8 gem install therubyracer -v '0.12.2' -- --with-v8-dir=$(brew --prefix v8-315)