Zooey Deschanel originally was cast as Mary but dropped out due to scheduling conflicts, and Rachel McAdams replaced her.
When Tim mentions that it's a long walk to Mary's car, he's not kidding. The distance between Joanna' flat and Mary's apartment is about 6 miles across central London.
When Tim first meets Mary, they are dining at a restaurant where the waiters are blind, and the diners eat completely in the dark, without knowing what they are being served. There is such a restaurant in London: Dans le Noir, 69-73 St. John Street, London EC1M 4AN.
Towards the end, Rory is reading the book 'Trash' which is Richard Curtis' next film. (Curtis wrote the screenplay for both this film and Trash (2014)).
The book Tim's Dad (Bill Nighy) reads out to Tim near the end is from Great Expectations by Charles Dickens, chapter 4.
Richard E. Grant, Richard Griffiths: As actors playing lawyers in the play, a nod to their roles as actors in Withnail & I (1987). This was Griffiths' final film role. He died three months before its premiere at the Edinburgh International Film Festival.