As a personal trainer, I hear it too often. Clients stepping on a scale and becoming overwhelmingly disappointed at the lack of weight they're losing.
Like I mentioned in my article on getting motivated, the key to tracking progress is through variation. Things like weight lifted, reps performed, time, body fat percentage, and of course: body weight are typical things to track.
The problem with tracking body weight is that there are far too many variables to consider for this to be a good measure of progress. Things like your hydration level, electrolyte retention, and how much food you are digesting can throw your weight off by 3 or 4 pounds in either direction.
Weight is just not the best measure of progress unless you're doing it once every month or so. I prefer much less frequency then that, as I ask for weight measurements maybe every 3 or 4 months from my clients.
Take for example, my trainee, Trey. Trey has lost 40 pounds of fat in about 8 months. Do you know how many times I had him weigh himself? Twice. Once when we began training and the second time was much more recent. The only reason why we did a second measurement is because he looks very physically different than when we first started. Having him measure his body weight was just a way for me to throw fuel on his passion for taking care of himself and to motivate him further.
Trey: 40 pounds lighter, but we only just recently found that out!
He went from not working out and being completely sedentary to constantly asking me for workouts and diet advice. I hooked him with consistency and gave light to the joys of putting in hard work and having discipline, not by slowly baiting him in with tiny tidbits of progression on a single data point, but by focusing on a bunch of smaller overlapping goals.
So that's it! Let the goals you and/or your trainer set be the guiding light in your transformation. Get off the scale and stay away from it unless you're sure that you're going to like what you see, otherwise you're setting yourself up for a whole lot of disappointment!