I'm sorry, but it always makes me twitch when someone says "muscle weighs more than fat." Because it doesn't. A pound is a pound is a pound (on earth anyway. Gravity, y'know). However, a pound of fat takes up more space than a pound of muscle does. Muscle is therefore more massive than fat. A square inch of muscle WILL weigh more than a square inch of fat (I'm pretty sure this was the example that helped me most when science class was trying to help me figure out the difference between weight and mass. It isn't a difference I'm likely to forget).

/end rant

:)