For those of you having your second child when you have a 2-year old, I just wanted to say I think it's great. I was 2 when my sister was born and we grew up doing everything together. We're still great friends even though we live so far away from each other.
My mom said I was jealous at first (I don't really remember), but I'm really glad I had my sister close in age. The jealousy will pass, but I'll bet it might be annoying in the beginning. I really think they'll appreciate it in the long run, though.