On his blog Martin Sikora shares a solution that many a Symfony developer out there might find handy for running their application in a shared hosting environment:

Some time ago (actually when I was making this blog) I posted on stackoveflow.com a question on how to configure Symfony to run on shared webservers where you can't change your website's document root. I solved it but forgot that I was asking and left it without any answer.

The main problem is that the DOCUMENT_ROOT for the hosting service can't be changed by the users of the shared host. To solve this he modified his routing rules (sfPatternRouting class) and changed his .htaccess file to rewrite things over from just "/page" to "/web/page" instead. A simple solution, but it might be evasive if you've never configured it before.