Your friends and family have gone to great lengths and expense to grace you with their wonderful gifts. It's time to say thank you! For gifts that have arrived on or after the wedding, tradition dictates Thank You notes are sent within three months. Personally, I think three months is a very long time to acknowledge a gift. If you receive your gifts before your wedding, you should thank the recipient within two weeks. I like that timeframe-- it's much more cordial.
Thank you notes can be flat or folded but must always be handwritten. Never, under any circumstance do you ever send a pre-printed thank you note. Even if you have 300 guests giving you 300 presents at your wedding, you better believe you need to handwrite 300 separate thank you notes. Just one reason to keep your wedding small I suppose! One of my favorite passages in Emily Post's Etiquette book from 1934 says this regarding pre-printed thank you notes. It's true, but quite funny in its tone: