Greg Beaver has blogged about an enhancement in the latest release of phar (1.2.1) - a major speed boost:

A few minutes ago, I released phar version 1.2.1. phar is a PHP extension that allows the creation of complete filesystems within a single physical file. In addition, a bootstrap stub written in PHP can be used to run a phar archive as if it were an executable file or shell script. Documentation on its usage and how to create phars is at http://php.net/phar in the PHP manual.

Greg mentions some other issues that were fixed and a refactoring of some of the stream operations to cut the speed in half.