Drush installation problem - Non-empty values for magic_quotes_gpc
Be sure you are editing the right php.ini file. As far as I recall the file used from PHP CLI could be different from the one used from PHP when running as Apache module; plus, Drush could use a completely different file, basing on its options, or settings.

To see which php.ini file Drush is using, use drush status. Drush can use a php.ini file that is saved in the $HOME/.drush, or /etc/drush directory; it can also use a drush.ini file present in the same directories. Alternatively, the path of a php.ini, or drush.ini file to use are taken respectively from the PHP_INI, and DRUSH_INI environment variables. (See the content of the README.txt file for more information.)

The function that checks the PHP settings in the php.ini file is _drush_environment_check_php_ini(), which contains the following code.

  // Test to insure that certain php ini restrictions have not been enabled
  $prohibited_list = array();
  foreach ($ini_checks as $prohibited_mode =&gt; $disallowed_value) {
    $ini_value = ini_get($prohibited_mode);
    $invalid_value = FALSE;
    if (empty($disallowed_value)) {
      $invalid_value = !empty($ini_value);
    }
    else {
      foreach ($disallowed_value as $test_value) {
        if (strstr($ini_value, $test_value) !== FALSE) {
          $invalid_value = TRUE;
        }
      }
    }
    if ($invalid_value) {
      $prohibited_list[] = $prohibited_mode;
    }
  }


On my computer, the directive for which the error message is reported is set with the following line.

magic_quotes_gpc = Off


When I execute dpm(ini_get('magic_quotes_gpc')); I get 0 as output.