Alice Dinnean, the puppeteer who operated the baby demons, also operated the living mummy hand in Life Serial (2001) and the Angel puppet in Smile Time (2004).
When Buffy breaks up with Spike, she calls him "William" for the second and last time, the first time having been in No Place Like Home (2000), when she found Spike lurking outside her house.
Buffy says "I have a house, I think it's safe, sometimes you can't leave" referring to her birthday party in Older and Far Away (2002).
At one point, Riley says, "The wheel never stops turning." This mirrors another Jos Whedon led show, Firefly. In the pilot, Malcolm Reynolds famously says, "The wheel never stops turning, Badger."