Interesting article on Apache logging
There is a really nice article on ONLamp: Profiling LAMP Applications with Apache's Blackbox Logs. Most Apache users accept the default logging configuration and often never realise exactly what is going on. This works when things are going well, but not so much when a problem arises and needs to be troubleshooted. In the article, Chris Josephes explains how to make the most of the Apache logging facilities.
It is surprising how little people talk about logging, given that data is essential for forensic analysis. One of the reasons I initially created mod_security is to allow me to see the contents of POST requests.