AIM not withstanding, I think it's fine to say "thank you" or "g'day" when an acknowledging call was required anyway... but it's not fine to say "thank you very much, y'know i'm awfully glad you're here doing what you do. Now I'm gonna head on down souf and enjoy the skies; you have a mighty fine day, y'hear?"I picked up the habit of saying "thank you" from one of my CFIs.