I am on my 7th Week of P90x, I see tons of difference.
Lost 5 inches off waist, lost 20lbs. I begin to see top 2 packs. =) I was 200 and 38" waist. 5'9"

I have not had a single day off from start. I thought x stretch was useless, so I did cardio x instead. It seems to be working for me. However, is it necessary to take a rest day? I always wondered...

I wouldn't think its necessary, especially as you move and become stronger. I enjoy a day off but if I was going to sub it with something it would be a quick yoga workout (40 mins). Still get good stretching in and a good sweat.

The thing is, your muscles/joints/etc only grow and repair at rest. its doesnt grow when you're working out. if its been working for you, great, but just becareful. it may eventually lead to injury...

good job so far, keep it up!

Isn't that why we work out different part of our body everyday? So that we have time for muscles to grow for a specific part of body with a couple of days of resting in between different work out scheme. I thought that was what muscle confusion was all about. no?

It is more about getting a rest day in for body to recover as a whole. Also I believe to keep you sane. In the beginning easy to go 7days a week when you are fired up. You will welcome a rest day later in the program.

X-Stretch useless? Wow.