JD's fantasy sequence with his son and the espresso machine is a spoof of similar anti-drug PSA's that ran on television in the 80's.
This episode contains numerous references, gags, and plot points featured in prior episodes, in some cases recreated word-for-word.
When the Janitor and Troy are trying to figure out the riddle, the Janitor says he went to Yale. When trying to figure out the same riddle in "Scrubs" (2001) {My Lucky Night (#3.4)}, he says he went to Harvard.
The first 8 seasons were filmed in North Hollywood Medical Center, a decommissioned hospital.
In the scene with "floating head doctor", when JD and Dr.Cox are first seen walking and talking together, you can see the silhouette of a second body on the left hand side.