Addressing Thank You Notes
Thank you letters should be addressed to the individual(s) who signed your gift card. In the case of a gift from a family, the envelope can be addressed to Mr. and Mrs. Pilato, and the salutation can be "Dear Donna and Joe." You can make reference to the remaining family members in the body of the note: "Please extend my thanks to Gina and Marie, and let them know how much I am enjoying the book."
The formality of your salutation should be based upon your relationship with the person whom you're thanking. For example, in the case of a thank you for a job interview, the salutation should read "Dear Ms. O'Brien" unless Ms. O'Brien gave you permission to address her by her first name. Similarly, a thank you for a wedding gift received from friends of your parents should be addressed to "Dear Mr. and Mrs. Cohen" unless you grew up calling them by their first names.
When composing a thank you note for hospitality, you may simply address it to your hostess (assuming she's the person who did the work), but include a thank you to the husband in the text: "Please let Aldo know how much we appreciate your gracious hospitality and his very amusing stories during dinner."