Writing the perfect thank you note takes time, practice, and a lot of thought. After receiving wonderful holiday gifts, we all want to thank the special people who gave them. Somehow a thank you e-mail to Grandma just doesn't seem satisfying enough.
If you need help finding the right words, you may want to read the book Just a Note to Say...The Perfect Words for Every Occasion, by Florence Isaacs.
Be sure to read this piece by Leslie Harpold on How to Write A Thank-You Note. It is brief, to the point, and offers many good tips on the subject.
To put things in perspective, read The Essential Handbook of Victorian Etiquette to learn about very demanding social etiquette of an earlier time.