Yes! With both my kids, I was back to pre-pregnancy weight by 3 months postpartum. By 6 month post-partum, I was actually below and stayed below the entire time I was nursing - all the while eating huge meals to take int those extra calories to make milk. I'm convinced the nursing really helped me lose the baby weight.
Where I got into trouble the first time was that I was eating extra to maintain my supply (even though I lost all the weight). And when the baby weaned at 13 months, I forgot to stop eating extra and I put on about 10 pounds pretty fast. With baby #2, I had learned that lesson, and when he weaned at 18 months, I watched what I ate (didn't diet, per say, but ate normally instead having huge meals) so that wouldn't happen again.
Also, if you have gained 30 lbs total, you won't have 30 to lose after the baby is born. at least 15 of that is gone when you have the baby - 8 lb of baby, 5-8 lb of all other stuff - amniotic fluid, water retention, placenta, etc. So you'll probably only have about 10 or so to lose once the baby is born. Not a big deal even if you don't lose all of it in the first 6 months!