When sending invitations, is it alright to include a little slip of paper saying where you are registered at...or how do you handle that?

It isn't proper etiquette to include gift registry information or enclosures with the wedding invitations, as it implies a gift is expected. Family members, attendants or close friends can spread the word to other guests in person, over the phone, or by email, if asked. Or, if you are asked where you are registered, you can certainly tell them then. You can, however include registry cards in shower invitations, since giving gifts is the reason for a shower. Many stores provide you with registry enclosure cards for showers.