I got p90x as a gift so I did it, but it took me about 110 days to finish it since I skipped some days.
I got good results . The program is good, solid, and thorough in many different areas of fitness including resistance training(weights), cardio, yoga, stretching, boxing-type workout, and calisthetics.
The program is good because it keeps you motivated to work out. You can get similar results without doing the program. heck you can even do the exact program without watching the tapes. But I believe it's main attribute is to keep people motivated.