congrats Kim!! i think it's VERY exciting!! and i think it will be lovely for your kids to have siblings close in age... and the people who scoff at the idea are just jealous that you have enough energy to give to two young kids at once! it makes them feel inadequate (although that's all in their head, and nothing to do with you)... i'm PG with #1, and would love to have the rest of my kids in close succession..
i'm the first of all my friends to become PG (even though i'm really not THAT young), and i can see a few of them thinking "what have you done? your life is over" - but i'm SO excited about this next period of my life - at the end of the day i don't think there's anything more important than family!!