P90X is an excellent system. It will definitely help you break a plateau. The upper body and core work are especially effective. And the rotations (at least the "classic" and "doubles") are very well thought out and effective. (The lighter rotation is unbalanced, IMO, and every week, there is a body part missing from the weight work).
This was definitely my best purchase of last year.
As Carole says, do a search (in the "Open Forum") and you'll find lots of info about it.
ETA: I just caught the end of the title of your thread (cut off). For losing weight, P90X might not be the best. It's strength is in muscle and strength building and balance (including core and stretching/yoga). The cardio is moderate, intentionally so--to keep from burning up the muscle you are tryinig to build. You could make P90X more weight-loss friendly by addiing some Cathe cardio in place of P90X cardio (like IMAX2).
And if you don't already have Cathe's interval workouts, I highly recommend IMAX2 and Interval Max once a week (twice, if you can take it!) to help mix things up and take you a step beyond. Interval workouts are excellent for this. "Cardio Coach" is another program of interval workouts on CD that works for any kind of cardio equipment (steppers, treadmill, stationary bike). And if you have a spin bike, "Spinervals" DVD's are some very effective and tough spinning workouts that many people find effective and fun.
Also: often those "final 10 pounds" are more effected by diet than by exercise (or, more to the point, by a combination of diet and exercise). Not in the sense of "going on a diet," but in the sense of being mindful about what you eat, and avoiding high-fat, high-calorie foods that are nutrient poor, and focussing more on nutritionally dense yet low-to-moderate calorie foods (Ideally, ditch the processed foods, anything with white flour/high fructose corn syrup or corn sweetener, and hydrogenated oils in. Add a bid, raw mixed salad at the beginnind of both lunch and dinner, and emphasize veggies and fruits. )
...Carole