I was just thinking about this today, as it appears I have gained about 2 lbs in the past week.
No matter what your OB says, you should not be afraid of gaining 30+ lbs (unless you are already obese, but seeing as how many of us changed lifestyles when TTC, I doubt this is the case). During my first pg with DS, I was scared about gaining 'too much weight'. According to my OB at the time, 25 lbs was borderline too much. By the time I delivered at 34 wk, I had only gained 20 lbs. All of it was gone within 1 wk. I never deprived myself, but I know I did not eat enough and not enough of the right things, and to this day I believe one of the reasons I delivered prematurely was bc I simply had not gained enough weight and had a job where I spent 6 hours per day on my feet. My OB should have taken my job into account when telling me how much weight I could gain.
There's a reason that celebs gain 40+ pounds sometimes: they need to! As glamorous as their lives look, many are malnourished and don't get enough sleep. Actors at least work 12+ hours each day and spend several more doing interviews, commercials, traveling between work/home, etc. The only way to support a growing life with that kind of lifestyle is to gain that much weight.
So I've decided my former OB is insane to say that I, a sometimes frail-looking skinny girl, shouldn't gain more than 25 lbs. As long as you do it healthily (not eating whole pizzas or cartons of ice cream) and don't put yourself at risk for gestational diabetes doing so, gaining 30-40lbs should not worry anyone. If, God willing, my pg sticks I am going to aim for putting on 30-35 lbs. Bring on the full-fat dairy products. yum!!