Gonzalo Ayuso has posted a handy tip to his blog today about showing errors even with "display_errors" being off in your application (could be helpful in debugging those difficult problems).
Shared hosting are cheap, but normally they don't allow us the use some kind of features. For example we cannot see the error log. That's a problem when we need to see what happens within our application. Normally I work with my own servers, and I have got full access to error logs. But if we cannot see the error log and the server is configured with display errors = off in php.ini (typical configuration in shared hosting), we have a problem.
His solution involves an "error sniffer" script that captures the issues in a script and echoes them out at the end. In his ErrorSniffer he sets up a custom error, exception and shutdown handler to grab the problems and capture them for later use - including echoing them out to the user if desired.