In the lab, while Knox and Fred are examining the cyborg, Spike says "Sex with robots is more common than most people think." This is, of course, a reference to Spike's sexual relationship with the Buffybot that Warren Mears created for him.
Emil was previously mentioned in Spin the Bottle (2002), when Wesley tells one of his men that if the weapon he got works out in the field, Emil would be hearing from Wesley again.
Spike calling Wesley as "Percy" and referring to the Watcher's history as a "head boy" may be a reference to the Harry Potter character Percy Weasley, who was also a head boy.
Spike refers to killing his mother, who then, as a vampire, tried to 'shag' him. This is told in flashbacks in Lies My Parents Told Me (2003).
The destruction of the Council that happened in Never Leave Me (2002) is mentioned. However, we see that Wesley's father and other members such as Ronson and Giles have survived, so the organization may not be entirely gone.