Hey, It's That Place!: The block of flats where Clara's family are having Christmas dinner is the same one used in some shots of the Powell Estate in "Rose" (in particular, the long walking sequence leading up to the "turn of the Earth" speech).
History Repeats: Matt was recovering from a nasty leg injury while filming the final episode of his tenure. David Tennant also filmed his final episode while recovering from an injury, his being an ailing back that he'd recently had worked on with surgery.
The Other Darrin: Clara's father is played by James Buller in this episode, while previously in "The Rings of Akhaten" he was played by Michael Dixon. Of course, it works here because Clara's dad is 8 years older.
Real Life Writes the Plot: Matt Smith wore a wig; so does the Doctor. He also injured his leg on-set and the Doctor started using a cane.