Hey Natalie,
I've been reading this everywhere as well, and I've heard the same thing about it being poor etiquette. However, a large percentage of the wedding invites I've received over the years have had registry information on an insert card, along with
reception information, directions, etc. Since we've got a younger crowd coming to the wedding (maybe 6 people who don't get online regularly), we're planning on having insert cards for reception information, directions, and our website. Our
website will give information on where we are registered, accomodations, etc. The few family members who will not likely get online will most likely receive a phone call from a parent to see if they need any information that might be available online.
HTH.