One of the things that always stalls me in writing thank you notes is having the appropriate stationery. I used to keep a stash of monogrammed notes, but since baby came along, I find myself running out to buy kiddie notes.
Now I have a great solution for both of us. Papyrus sells stamps that you can customize with your initial so you can buy one for baby and another for yourself. I get plain note cards from Paper Source and then stamp them with the appropriate letter and write the note from there. That way I don't have to keep a separate pile of notes for each family member. And, to save yourself from having to write your return address each time, order an especially cute return stamp from them, too.