It's a given that thank-you cards should be sent when people come to your wedding and give you gifts. But the exact manner in which this should be done seems cluttered by a lot of rules and sometimes debate. I've seen some that are monogrammed in sealed envelopes and others that are just postcards, some with photos and some not. Some mention the gift (and some mention the wrong gift), and some add a personal note while others are more formulaic. What's okay and what's not? You tell me.