Thanks for this post! Drush now requires Composer for install, so I ran into issues using the manual method. The README.md is not 100% clear about how to proceed, so here's what I did.
First install Composer:
sudo curl -sS https://getcomposer.org/installer | php sudo mv composer.phar /usr/local/bin/composer
Next, install Drush:
composer global require drush/drush:6.*
Then follow the instructions here:
Don't forget to reload your bash_profile.