From what I saw when I visited the site a few months back, most of the information he posted was about corruption within the process of the Iraqi reconstruction, with no real classified information. Unfortunately, archive.org has no backup of the posts in question, but Google still links to an archive of several of his phone messages which mention his observations on the corruption within the Iraqi government. There are also two NPR stories on Leonard Clark that are worth listening to, for more of the back story.