Using drush on mac with mamp gave me some problems with default setup. I didnt set
DRUSH_PHP variable anywhere so default php was used, also with that no php.ini setting was set and in my drush status I got empty "Drush configuration" variable. So to set this up, I needed to add this to either .profile or to .bash_profile (depends of load order, later goes first if you have it)
export DRUSH_PHP=/Applications/MAMP/bin/php/php5.3.29/bin/php