The Illuminata - the diamond the nerds stole from Sunnydale Museum in Smashed - was on loan from the British Museum, where Giles worked before becoming Buffy’s Watcher. Willow mentioned this in Welcome to the Hellmouth.

Buffy writer Drew Greenberg told the BBC his feelings when he discovered that Amy’s de-ratting storyline would be in his episode (Smashed):
“I was excited too because I’ve been a fan of the show from the first episode myself, even before I was even working on it, so I’ve been waiting …

The trio of nerds reveal some of their weaknesses in Smashed: Jonathan is allergic to methane and Andrew is afraid of hot things.

Rick Garcia, who played the reporter in Smashed, is the sports anchor for Fox 11 10 O’Clock News. He has played reporters on many movies and TV shows including Collateral Damage, Shadow of Doubt, Volcano, Talent for the Game, 24, The X Files, Sliders, The A-Team and The Fall Guy.

Jack Jozefson, who played the security guard Rusty in Smashed, has also appeared in Bruce Almighty, Trade Day, Almost Dead and Lonely Hearts.

Adam Weiner, who played Simon in Smashed, also played a caged guy in the Angel episode ‘Disharmony‘.

Elizabeth Anne Allen, who played Amy, had the following to say about reappearing on the show:
“This year it just happened to fall together really brilliantly. I was available, they had an open space in their storyline and voila! They asked me and I said, “Heck, yeah”. I love it. …

Michelle Branch sings ‘Goodbye to You’ in the Bronze at the end of the episode Tabula Rasa. The song is taken from her platinum selling album ‘The Spirit Room’. The song was also played in the UPN promotion for the episode Empty Places. The lyrics are:

Of all the things …

The epic 1939 movie Gone with the Wind starring Clark Gable and Vivian Lee is referenced a couple of times in Buffy. In Tabula Rasa, Spike says to Buffy, “we kissed, you and me all Gone with the Wind, with the rising music and the rising… music”. In The Killer …

In Tabula Rasa, Xander says, “I just got back the memory of seeing King Ralph”. This was a movie made in 1991 starring John Goodman.

In Tabula Rasa, Buffy tells Giles, “I can’t do this without you”. She made the same statement to her Watcher when Giles confronted Angelus after he murdered Jenny in Passion.

In Tabula Rasa, Spike/Randy comes to the conclusion that he’s a noble vampire with a soul because he doesn’t feel the need to bite Buffy and he helps her to attack the other vampires. Buffy/Joan says “A vampire with a soul? How lame is that?” little knowing that her ex-boyfriend, …

Raymond O’Connor, who played the loan shark ‘Teeth’ in Tabula Rasa, has also been in April’s Shower, My Giant, Halloween 4, Six Feet Under, Days of Our Lives, Babylon 5, Sister, Sister and Beverly Hills, 90210.

Tara references the time when Glory brainsucked her mind in Tough Love when sings “you know I’ve been through Hell”, in the Under Your Spell/Standing Reprise in the musical.

Tara’s song “I’m Under Your Spell” in Once More, With Feeling is literal, as Willow placed an amnesic spell on her girlfriend in All the Way.