I installed the MAMP stack running PHP 5.4 on OSX Mountain Lion.
I uncommented the line in httpd.conf so I could use Symfony and restarted apache.
Yet when I browse to the Symfony home page, I continuously get 403 Forbidden errors.
I played with all sorts of httpd.conf and .htaccess settings to the point where I could access the symfony page (added FollowSymlinks), but when I attempted to run the online configurator (symfony/web/config.php) or the demo apps, I would only see blank pages in my browser.
Please help if you can, I had no such trouble installing on my laptop running OSX Lion.
Update: I installed the Symfony MAMP Stack with PHP 5.3 and had no trouble. This was also what I had installed on my laptop that ran OSX Lion.