I finished the program about a month ago (Stats: 36yr old, corp exec).  I really liked it but it is not for everyone. I would suggest you take their fit test to see how you fair. If you feel you need a foundational program to get into decent shape prior to P90X, I think Beach Body (the program makers) have a program called Power 90 (check out their site to be sure). Nonetheless here are the program pros and cons:

PROS (if you stay faithful to the diet and program schedule):

* You WILL loose fat - can't say I look like Michael Phelps but I am much leaner than when I was in Grad School (ate like a pig during class to keep awake due the 6hr lectures). Dropped 4 inches off my mid-section without reducing overall weight and chest is hard like when I was swimming everyday for a year.

* You WILL get stronger - I doubled my push up count and have a lot of functional strength (probably the reason I got off to a quick start on power hill climbing with the Trikke). Stamina is great too - cycle up the Santa Cruz mountains at pace, tough but you're at the top while others are looking at a lot of uphill asphalt.

* You WILL get more flexible - I used to cycle a lot but never stretched. The result was I could not bend over and touch my toes. Now I can palm my toes. Yoga X is crazy cool. Once you gain the balancing strength you'll feel like a stud (now I know why pro athletes say yoga or martial arts are an essential in overall fitness)

* BEST OF ALL - You WILL feel in control of your body. Clothes feel better, mentally you are refreshed, and you have a well of energy

CONS

* Gotta stay faithful to the diet and workout schedule - okay a break here and there is fine but this program is all about stressing the body at pace and consistency.  Pushing it 6 days a week for at least an hour is all they ask.

* You will suffer (I mean build foundational strength :-)) the first couple of weeks - If you think the program is easy, YOU are not working hard enough. Its all about taking your body to the next level. Where you are now is your baseline. The competition is old you vs. new you.

* NO you can't eat everything you see and like - to get the best results you are looking at one cheat night and the rest of the time you're eating a lot of protein

* Genetically not everyone is built to look like Tony Horton (the creator P90X) - Some people can get big arms and ripped abs relatively easy. Some can't. BUT, stay on the plan and you will get better and stronger.

OVERALL a great program. I have heard it said this is like having a personal trainer for 3 months. Once you open the videos you will know the mantra "BRING IT!"