The good news letter is a short thank you note I recommend you send to everyone in your network who helped you get your new job. It's best sent as a hardcopy note via the US Post immediately after you land the job. And if you have decent hand writing, make it even more personal by sending a handwritten message.
Alison Doyle recommends using the holidays as a time to send a Holiday Thank You Note to each person in your job search network. It's a good way to show your gratitude and stay in touch with those contacts you've developed. By the way, it's also an opportunity to ask if there's something you can do for them!