I was only able to do the P90X for a couple of days before life took control but the days I did do it I was very sore from my workouts. Which is good because pain means it's working, especially when you don't realize you had some of those muscles. The first disc I had to make some changes in the workout because I do not have access to a location to do chinups/pullups so I laid on the floor with 10 lb weights and did butterfly type exercises and switched it up a bit.
You are going to see results if you stick with this program, I have seen friends do it and seen the amazing transformations myself...