I think it's a good idea. Seems like these days people are trying to find any excuse to not send a thank you (like...I didn't have your address). I'm still a firm believer in thank you cards via the mail instead of email thank you's or phone, text, voice mail thank you's. If a person went out of their way to buy or make a gift for me, it's the very least I can do to acknowledge the gift with a thoughtful thank you note.