[raybbr]

As far as P90X I can tell you that I definitely got stronger and more toned, but I didn’t lose a pound.

Muscle mass is far denser than fat. If you lost some fat and gained some muscle the scale looks like you didn't lose any weight. That's a good thing.

[Altariel]

That’s my understanding, that the main thing to monitor is the number of inches lost, not pounds.