I gave this presentation to the pdxphp group.

Get a glimpse of what PHP is doing at its core and learn how to accelerate and/or troubleshoot those processes.
We’ll start with a description of some of the PHP internals to get a sense of how code caching and debugging work with PHP.
Then we’ll demonstrate installation, configuration and use of xdebug, APC, and Turck MMCache.

Slides are here