Disclaimer: This article isn't for fatties. Obviously.
When one goes to the gym, one is usually in pursuit of one of these three goals: aesthetics, to develop the body for sports (general), or strength training (leisure or competitive). None of which, should be based on the weighing scale.
If one is going for aesthetics, his concern should be on how he looks. Bruce Lee's highest weight was 165lbs/73kg, but I would dare to say he would look better than most people who weigh in at 180lbs. Frank Zane (see below) beat Arnold to the Mr.Olympia title despite being some 40lbs lighter. He continued to win three straight Mr Olympia titles despite being under 200lbs/90kg. Aesthetics is a subjective matter. If people are coming to you and giving you compliments, then whatever you are doing is working, be it the weighing scale telling you that you have gone up in weight or not. The only relevant objective measurement one can make in the pursuit of such a subjective goal, is the measuring tape.
If one is in the gym in order to become stronger and faster so as to enhance his performance in his sport, then it really doesn't matter how much he weighs, if he is doing better on the field/court. In such cases, the main goal is performance on the field/court, not the gym, or how much the bathroom scale moves. Never be detracted from your actual goal.
If one is in pursuit of strength, then it doesn't matter how much he weighs if his lifts are going up. In fact, it is obviously more impressive if one can lift the same weight at a lighter bodyweight. And this also bodes well for those who compete-lower weight class but higher lifts equal a better chance to win.
So don't be overly concerned by how much you weigh. Remember, the reason why you're in the gym is not because you want to change your weight!