Ian says that the first time that Sherlock ever saw Alistair perform, it was as Vladimir in Samuel Becket's play Waiting for Godot. In fact, not long before filming this episode, Roger Rees(who plays Alistair) had played Vladimir in a highly acclaimed production of Waiting for Godot opposite Ian McKellen (as Estragon).
The lines quoted by Alistair ("At me too someone is looking...") are from Act 2 of Beckett's Waiting for Godot, the play in which Sherlock first saw Alistair perform.
The title "No Lack of Void" is also a line spoken in Beckett's Waiting for Godot. In the play the phrase speaks to the repetition and emptiness of the main characters' lives.
Similarly, Sherlock has expressed more than once that time and tedium challenge his happiness and often his sobriety
Holmes states that the average stride length for a 5ft 11in man is 1.8 meters. That would be a stride length equal to that of his height. The actual stride length is around 2.5ft (76cm)