My first pregnancy I gained 18, then lost 6 in my 3rd trimester, and ended up gaining 12 lbs total, and going home at or just below my preprgnancy weight right after delivery. I was super sick the entire pregnancy, I wouldn't recommend it...
All of the others I've gained 35-40 lbs, and always lost it within 6-8 weeks. My sisters aren't thrilled with me about that, but I'm sure not complaining.
Ok, I think I kept 5 lbs or so from number 7... metabolism slowing down in my old age, I guess...