I'm am crashing from the Sept DDC, but I can chime in with my weight loss with all 3 kids.
With DS1 I gained about 35lbs, 15 lost by the time I came home from the hospital, and another 10 within the first two weeks pp. I started Weight Watchers at 2 weeks pp, and added exercise when I felt up to it and actually lost the last 10lbs by 7 weeks pp. I lost all the weight, but body took a while to look the same, hips shifting back to normal, etc.
With DS2 I actually started out in better shape, worked out throughout my pregnancy, but gained 40lbs. I lost about 15 again by the time I left the hospital, another 5 in the first few weeks, and had to really bust my ass to lost the last 20 through weight watchers and doing a lot of StrollerFit. It took about 4 months to lose it all.
With DS3 (4 weeks old now!) I gained 40lbs again, although I was in MUCH better shape to start, worked out until the day I delivered, did a lot of pilates etc. Lost 20ish lbs the first couple of days, and another 5 in the first two weeks. I just started WW and getting seriously back to my workouts this week and I have dropped another 5 lbs. So at 4 weeks pp I have about 10 to get to my pre-pregnancy weight, although ideally I would like to lose another 5 beyond that. The real trick is getting to look the way I did pre-pregnancy. I anticipate doing a LOT of pilates and cardio in the coming months.
I find myself having to start getting very serious about weight loss and diet within the first month otherwise I'm afraid I will settle into my new size and invest in clothes and make it too easy to keep the extra weight on. That is especially important ot me this time around with the holidays and all the good eating opportunities looming in the near future.