Hi everyone. I've released a plugin that does some readability analysis on posts.
Word Statistics Plugin
It is easy to install, works with WordPress 1.2, doesn't require you to edit any files, and computes the Gunning-Fog, Flesch-Kincaid, and Flesch readability indexes for the post being edited. See the site for installation instructions and more information about readability anslysis.
The plugin is officially a beta (test release) but it is stable. I've been using it for a few weeks.