Duck's dog, Chauncey, is an Irish Setter.
The song playing during the opening scenes of Peggy, Joan and Betty dressing is The Infanta by The Decemberists. The song is on the Picaresque album, which was released in 2005.
Joan: You want to be taken seriously? Stop dressing like a little girl. (advises Peggy when she complains about not being included in after-hours business discussions)
When Don calls Bobbie at her hotel, she tells him that Jimmy will be spending the next ten days performing at The Beverly Hills Supper Club. The Southgate, Kentucky club really did exist and in fact was the scene of one of the worst fire-related tragedies in American history. When it burned on May 28, 1977, 165 guests were killed and more than 200 were injured.