Quite frankly, 2nd and 3rd (and more showers) are rather tacky, and registries as a whole are tacky. The point of a baby shower is for people to celebrate the blessing that is your upcoming (or already had) baby not for the mother or mother-to-be to be a present whore. Prior to WWII baby showers were held AFTER the birth, so everyone could meet the baby and celebrate it's birth. Which is the tradition my family still holds to. Any subsequent "showers" to number one should be a baby welcoming party.
Parties are not for you to get gifts. Your guests should feel honored to be invited and be a part of this wonderful time in your life. They are not there to be responsible for buying childcare items for the child you chose to get pregnant with.
I will have a Babies R Us registry, but only for my own use, discounts, VIB card, and completion discount. If you have a registry, it's SUPER tacky to put it on the invitation. That's basically commanding your guests to buy you a gift and to buy what you tell them to. How RUDE!