This post is from 2009 but for anyone considering a career teaching in a private/public school, you may want to check out the following blog maintained by a high school history teacher. He (was) is specifically looking for Ph.D.'s to apply to open positions at his school and offers some advice and words of wisdom to prospective applicants.
An even older post (2004), by a former public high school teacher/blogger, offers a critical look at the current certification process in the U.S. public school system. While Ph.D.'s may be great teachers, we're hampered by the requirements imposed upon the educational system at both the state and federal level. Interesting food for thought . . .