"Your command line PHP installation is too old"
I had a similar problem and I was able to specify what version of PHP Drush will use by adding the following to my .bash_profile file:

export DRUSH_PHP=/usr/local/php53/bin/php


That got mine working.  I had tried a more general approach where I specified PHP 5.3 for my command line generally, but this didn't work.  Specifically targeting Drush is what it took for me.