I just got in the sandbox with symfony 1.4 & php 5.3.3. In the beginning everything went well, untill I tried to pull some data from a database. I got this error:
PDO Connection Error: SQLSTATE[HY000]  No such file or directory
Error log said:
PHP Warning: PDO::__construct() [<a href=‘pdo.–construct’>pdo.–construct</a>]:  No such file or directory (trying to connect via unix:///tmp/mysql.sock)
It made it clear that mysql.sock was missing or I had some configuration problems. Turns out my php.ini file had to be changed a bit.
Find out where mysqld.sock or mysql.sock is residing and change the default value in your php.ini. That should solve the problem.