I have my big U/S! Beyond being excited for that, the 18th also is my son's 3rd birthday! My DH and I are both planning on taking the day off to celebrate the birthday with a pool trip (he has two parties planned, one with family the weekend before and one with friends the weekend after), and a present and cake, and then we are all going to the U/S!
Also, every time we go shopping, my DS finds these cute baby outfits (all girly BTW) and asks if he can buy them for "his baby." So, once we find out what the baby is, after the U/S, we will take him to the store and let him pick out an outfit for "his" baby. I'm so excited for the parties, the big U/S, his birthday, everything.