If you want to run Drupal on localhost on Mac OS X Lion with the clean url feature enabled you have to edit the ‚httpd.conf‘ file located under ‚/etc/apache2‘.
1.) BACKUP THE ORIGINAL httpd.conf !!!
2.) Go to the ‚/etc/apache2/‘ folder
3.) Open the httpd.conf file with the editor of your choice with administrative rights e.g. sudo mate /etc/apache2/httpd.conf
4.) Locate the <Directory /> directive and change ‚AllowOverride none‘ to ‚AllowOverride All‘.
5.) Locate the <Directory „/Library/WebServer/Documents“> directive and change ‚AllowOverride none‘ to ‚AllowOverride All‘.
6.) Restart the web server