I try and send out thank you cards as much as I can. We sent them for our wedding, baby showers, and we even send them for things like people doing us a favor. I've been slacking a bit since LO was born. I didn't send out as many as I should have for the gifts we received after she was born. I vow to get back on track though! I think expressing thanks is very important. I have received maybe 3 thank you notes from others in my entire life, and even verbal thank you's (which go a long way), are becoming rare in my life from others.