Okay. I'm not here to second guess anyone's program (unless it is unsafe). ANY program that gets someone up and moving is a good one. But this appears to be a push-up progression plan and not a fitness plan per-se.
As a general rule, one should not focus on one and only one exercise. This is particularly true when that exercise moves in only one plane. You run the risk of over-taxing one set of muscles or under-developing another. Both can lead to injury.
Please do not misunderstand me. I love push-ups and do them almost daily. They are an excellent upper body exercise, they require no equipment, and the provide a measure of progress, but push-ups alone are not an adequate exercise program.
For those who have begun following this program, I would suggest looking at http://forum.deeranddeerhunting.com/tm.aspx?m=22014 or http://forum.deeranddeerhunting.com/tm.aspx?m=23375 in order to get some additional ideas on things you can work in as well.
Again, I am not knocking the 100 push-up program, I am just suggesting diversity.