In this new post to his blog about the APC caching tool that can speed up your PHP applications dramatically when used correctly. Brandon recommends a tweak that could help it go even faster.

The very first thing that APC does when it's turned on is begin caching the opcode output from all of your PHP files. [...] Also by default, APC checks the file on the file system to determine if it has changed since the last time APC cached the opcodes. When APC does this, it executes a file-system-level stat() call, which in the scheme of the calls performed is expensive.

There's a setting in your php.ini to take care of this (you might have to add it in) - apc.stat - that can just be set to "FALSE". There are some drawbacks he points out, though like restarts required for clearing the cache and the fact that, no matter what you do, bad code will always run badly.