On the Coding.bmail.net blog they've posted a guide to what they've called an advanced logging system in PHP for careful developers - essentially a logging system that's as "error proof" as possible and that works with as little user exposure as possible.

Being aware of all the activity and problems under the hood is essential when running big websites with lots of users, many features and, as it is usual in such cases, weak spots that must not be left untracked.

In order to be the first in knowing when errors or other events of interest happen we need a well designed logs manager. My code will provide such a feature, for PHP based websites.

They briefly outline how the complete setup will work, failing back to email if the database connection isn' available and logging based on environment. It also includes error levels and, on development only, a method for showing the errors being logged. While a good bit of this functionality could be handled by something like Monolog they do include some additional features like the email fallback, output of the errors in development mode and custom error/exception handlers.