When Harry Crane is eating a Stick candy in Pete Campbell's office it's full one minute then half gone then full again.
The exterior of Don Draper's house is first shown at the end of episode 1, season 1. In episode 3, season 1, the exterior of the house is shown again - only it is a completely different house now. The house in the first episode has dormers on the roof and a small portico. The house in the third episode does not have any dormers or a portico. The window size and position are also different.
During the party scene, a radio announcer introduces a opera broadcast of Mozart's Marriage of Figaro as staring Robert Merrill and Joan Sutherland. Neither Robert Merrill or Joan Sutherland included leading roles in Figaro in their repertoire.