i sent thank you letters to all the places i interviewed at (except columbia). at BU i sent an e-mail thank you's because i was so sick and tired of writing out letters and mailing them. BU was the only place that responded to my thank you letters (via e-mail), and in a few of my letters i mentioned the fact that i was congnizant of the fact that letters of this sort were always a bit cliche and contrived.