Full credit for this one goes to my wife. When you think about it, the phrase "You look [insert attribute that is greater]" is either a remark from an incredibly perceptive individual, or a testament to how little that person thought of you since you last met. "You look like you've lost weight" means "man, I remember you being fatter than you are right now". On the flip side, "You look like you've gained a little weight" is nice in the thought that they had a great mental image of you beforehand, but they're still calling you fat.