Do people still send thank you notes? It's a good question and while most actually written correspondence especially among friends and family has gone the way of the email, a thank you note whether it is hand-written or electronic is an indispensable and EASY way to make sure you look like the star that you are. Thank you notes are almost mandatory in the job search. A well-written (and I mean hand-written) thank you note sent after an interview is the perfect way to show your potential employer that you are thoughtful, and that you are focused on the importance of appearance, details and follow-through. Also this will really differentiate you from everyone else. The employer will think if you are this thoughtful about the interview, think how thoughtful you will be about the job!
On the personal side, whenever anyone goes out of their way for you whether it be treating you to a gift, a lovely dinner (homemade or out in a restaurant), or did something special for you, sending a thank you note is THE best way to make sure they know their effort was appreciated. They did something nice for you and of course you said thank you on the spot, but sending one more thank you in the email (email or snail mail) really makes the difference and makes them glad they went the extra mile.
The salutation - This would be how you address the person inside the card or note. Dear..., For..., To.... Any of these is perfectly appropriate; Use what feels right.
Thank them for the gift/gesture/whatever-Thank you for...the lovely dinner, the beautiful sweater, helping me move. Whatever it is, make sure you include the thank you AND what you are thanking them for.
The how did they impact you part-People love knowing that you like what they did for you or gave you. Acknowledge their gift and something about how you plan on using it, or how their efforts helped you. For example: "Thank you for the great gift card. I am really excited to go out and get myself that treat I was telling you about". Or, "Thank You so much for helping me move the other day. You really made everything so much easier and I am loving my new place." That's the basic idea.
4) The close-"Sincerely", "love", "See ya soon", just include something nice to sign off with.
The question about when do you send them? As soon as possible is ideal. I had read about a woman who has blank note cards on her bedside table to write thank you notes before she goes to sleep. I don't do that. But I do have a few tucked in my office desk drawer and at home so I can do them as soon as I get a chance and not forget. There are always a few extra minutes to be thoughtful, and really there's never a statute of limitations on being thoughtful.