It is never okay to add a gift registry card to your wedding invitation suite.
According to Peggy Post, wedding invitation etiquette: registry and gift giving information is spread by word of mouth or can be given by inserting into a shower invitation. This information should NEVER grace the wedding invitation. This puts to much emphasis on the gift and not the guest attending which is the most important part of your inviting and hoping the guest can actually attend. Inserting such information can be a turn off for your friends and family. Gifts are the guests choice.
Adding a gift registry card in with or on your bridal shower invitation, that is a different story. The person giving the party is allowed to give their guests gift ideas FOR YOU! Parents, grandparents, aunts and bridesmaids can verbally tell the guests gift ideas when asked.
Growing in popularity among brides and grooms is the creation of a wedding web site. This would be an acceptable place to provide a link to your Registry.

Getting Started
In addition to registering for fine china most couples pick out a set of dishes that they’ll use every day. Choose a midprice pattern that you won’t tire of and isn’t likely to be discontinued. If you fall in love with dishes from a seasonal line at a mass-market retailer, ask if you will be able to purchase more later on.
Assessing Your Needs
12 settings of informal china are adequate, unless you know you’ll be entertaining large groups. Think about what you’ll really use. Many couples register for four-piece place settings of informal china, including a dinner plate, salad plate, mug (in place of a cup and saucer, which are rarely used daily anymore) and cereal bowl (in lieu of a soup bowl).
Cost and Quality
Because the cost of everyday tableware is relatively easy on the wallet‚ you can afford to be more creative with the products you register for, and even integrate informal dishes with higher-end pieces.
Notes on Care
Consider registering for earthenware and stoneware, which are made of clay and often glazed or brightly decorated. Earthenware is susceptible to chipping, while stoneware is chip-resistant. Most clay-based china and glass, is ovenproof and dishwasher- and microwave-safe. Plastic, wood and bamboo pieces are attractive additions to the table but generally not heatproof.
Something Extra
Certain accessories (like salt and pepper shakers) look just as nice on a fancy dinner table as they do in the morning at breakfast. Register for such pieces (serving bowls too) that work in more than one setting.