The New York Times has an article on Tony Horton and his P90X system. The article is mostly about infomercials and selling of the system, rather than the system itself.
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However, the article is worth it just for his pushup explanation. He teaches you how to do a pushup. His cue on correcting anterior pelvic tilt (not that he calls it that) and how to prioritize form over reps and depth is excellent.
You can access the video (hopefully) by clicking here