Install issues via composer
I did a work around without using composer to do the install by doing the following:


make a drush directory in your home folder (~)
git clone https://github.com/drush-ops/drush.git
cd into that directory
./drush --version (it should complain about composer install)
run composer install
./drush --version WORKING!


I'm using ubuntu so initially I did apt-get install drush, but that version is 5. Then I did the following to download the latest into ~/drush 

From there I went to my global run folder: /usr/bin and renamed the old drush to drush_old and then did a ln -s ~/drush/drush drush now its on the latest drush!