From www.theknot.com
Q.
Is it appropriate to register in time for our engagement party? I have been told that it's a social no-no to register this early.
A.
It's perfectly acceptable to register as soon as you get engaged. This gives guests who'd like to purchase a gift for you for any prewedding parties -- including engagement parties, showers, or brunches -- some guidance when buying. The fact that you are registered does not mean that guests must buy a gift from your registry, it simply gives them options. One thing to note: Do not include registry information in your engagement party invitations or in any other formal manner -- this is considered bad etiquette. Word of mouth is really the only way to inform guests about your registries -- and even then, only when they ask. Remember, giving gifts, while certainly customary, is not mandatory for engagement parties.