The Greek word "amara" means "eternal" so the "Gem of Amara" means "The Gem of Eternity".
We see in Buffy's yearbook that Harmony's last name is Kendall. Interestingly, the character Sarah Michelle Gellar played on All My Children was named Kendall — perhaps this is an inside joke.
Buffy and Willow's dorm room is number 214. We have seen glimpses of the number in previous episodes, but this is the first time that we have seen it clearly.
We see that Buffy has a scar from when Angel fed from her. But before this there has never been any mention of The Master feeding from her and as far as we can tell she has no scar from that encounter.
The scar that Parker is looking at is also where The Master bit her. The Master, Angel, and the third person to bite her all bite on the same side and acoording to the scar in the same spots.
Parker's comment about casual sex mirrors Angel's comments to Buffy when he lost his soul after they made love.
When Spike shows Buffy the Gem of Amara at the end when they fight, it appears that he is showing her a silver skull ring.
Nitpick: When Buffy is talking to Parker on the college campus, there are students everywhere. All of a sudden, Spike shows up to fight Buffy and there are no more students in sight.
Goof: While Spike has on the Gem of Amara, Buffy stakes him, but a few scenes later we see a full body shot of Spike and he doesn't have any hole in his shirt.
Goof: The necklace that Spike thinks is the Gem of Amara reappears around his neck after he throws it off.
Parker: I mean, everybody says they get it. "Oh man, me too. Live for today." But what they really want is an excuse to goof off and not study for finals.
Buffy: Also a valid life choice.
Spike: Listen to me, you stupid bint. This gem is everything. I came back to Sunnydale for it, a place which has witnessed some truly spectacular kickings of my ass.
Xander: I'm not enjoying this.
Giles: Well, shelve them correctly and we can finish.
Xander: I just don't get your crazy system.
Giles: My system? It's called the alphabet.
Xander: So, the crux of this plan is...
Anya: Sexual intercourse. I've said it, like, a dozen times.
Xander: Uh huh. Just working through a little hysterical deafness here.
Anya: I think it's the secret to getting you out of my mind. Putting you behind me. Behind me figuratively. I'm thinking face to face for the event itself.
Anya: So, where's our relationship going?
Xander: Our what? Our who?
Spike: So, you let Parker take a poke, eh? Didn't seem like you knew each other that well. What did it take to pry apart the Slayer's dimpled knees?
Buffy: You're a pig, Spike.
Spike: Did he play the sensitive lad and get you to seduce him? That's a good trick if the girl's thick enough to buy it. I wonder what went wrong. Were you too strong? Did you bruise the boy? I guess it doesn't matter. You were never worth a second go. Come to think of it, someone told me as much. Who was that? Oh yeah... Angel.
Willow: Did it happen with Parker?
Buffy: Yeah, it happened.
Willow: Well, and? Details! I mean, not details, I don't need a diagram. But, you know, like maybe a blurry watercolor.
Willow: He's a poop head.
Buffy: You're right. He's manipulative and shallow... and why doesn't he want me? Am I so repulsive? If there was something repulsive about me, you'd tell me, right?
Willow: I'm your friend. I would call you repulsive in a second.
Buffy: Maybe Parker and I could still work it out. Do you think we could still work it out?
Willow: I think you're missing something about this whole "poop head" principal.
Oz: Okay, either I'm borrowing all your albums, or I'm moving in.
Giles: Oz, there are more important things than records right now.
Oz: More important than this one?
Giles: Um, I suppose an argument could be made for...
Xander: Whoa, Giles has a TV. Everybody, Giles has a TV! He's shallow like us.
Oz: I got to admit, I'm a little disappointed.
Willow: Well, maybe it doesn't work. It's like art.
Spike: The Gem of Amara. Official sponsor of my killing you.
Parker: You think I could get a dance with the prettiest girl at the party?
Buffy: And what do I do, just stand here and watch?
Xander: But sexual interc- What you're talking about, well- and I'm actually turning into a woman as I say this -- but it's about expressing something. And accepting consequences.
Anya: Oh, I have condoms. Some are black.
Xander: That's... that's very considerate.
Anya: I like you. You're funny, and you're nicely shaped. And frankly, it's ludicrous to have these interlocking bodies and not... interlock. Please remove your clothing now.
Xander: And the amazing thing... still more romantic than Faith.
Spike: We've got an extra set of chains.
Harmony: Ew. Just because Dorkus went in for that...
Spike: Say her name.
Spike: Bite your tongue.
Harmony: Do it for me.
Harmony: Hey, I don't have a pulse. Cool! Can we eat a doctor so I can get a stethoscope and hear my heart not beating?
Harmony: Is Antonio Bandaras a vampire?
Harmony: Oh. Can I make him a vampire?
Spike: No. Wait. On second thought, yeah. Go do that. Take your time. Do Melanie and the kids as well.
Bufffy: What's the matter, Spike? Dru dump you again?
Spike: Maybe I dumped her!
Harmony: She left him for a fungus demon. That's all he talks about most days.
Buffy: This is it. My door. Wood. Maybe some kind of wood veneer.
Oz: Devon dated her for a while, but she was too flaky for him, which, stop and marvel at the concept.
Buffy: Guy dating Harmony dead. Must be, like, the most tolerant guy in the world.
Anya: I can't stop thinking about you. Sometimes, in my dreams, you're all naked.
Xander: Really? You know, if I'm in the check-out line at Wal-Mart, I've had that same one.
Anya: So I can assume a standing Friday night date, and a mutual recognition of prom night as our dating anniversary?
Xander: Anya, slow down. In fact, come to a screeching halt.
Parker: I'm not doing the deep "get sympathy" routine. I mean, don't you just hate guys who are all, "I'm dark and brooding, so give me love."
Buffy: I don't think I've ever met that type.
Devon: That was, like, the best set ever. We'll do great in LA. We're gonna have them glued to their seats.
Willow: Uh, Devon? Aren't they supposed to dance?
Oz: Well, we can glue them to the dance floor.
Devon: I don't mean with real glue. You got that, right?
Oz: I got that.
Willow: Buffy's looking at Parker, who, it turns out, has a reflection, so big plus there. Buffy's having lusty wrong feelings.
Buffy: No, I'm not.
Willow: No, you're not.
Buffy: Oh, I so am.
Harmony: Being a vampire sucks!
Anya: You should lock your door.
Giles: Believe me, I am kicking myself.
Harmony: You love that tunnel more than me.
Spike: I love syphilis more than you.
Buffy: Harmony is a vampire? She must be dying without a reflection.
The song "It's Over, It's Under" by Dollshead plays while Buffy searches for Harmony, Spike breaks through to the crypt, and Buffy waits for Parker to call.
The album that Giles and Oz bond over is "Loaded" by The Velvet Underground.
Intentional or not, this episode begins a tradition of Jane Espenson writing the third episode of each season ("The Harsh Light of Day" (4x03), "The Replacement" (5x03), "After Life" (6x03), and "Same Time, Same Place" (7x03).)
This episode opens with a Bronze performance of Dingoes Ate My Baby. The previous episode closed with their song "Pain" playing in the background.
Bif Naked performs "Moment of Weakness" and "Lucky" at the campus party where Buffy runs into Spike and Harmony.
In this same year  Terminal Reality released the horror computer game Nocturne in which one of the missions of "The Stranger" is to recover the "Yathfoe-Gyuole stone" a.k.a. "the vampire holy grail" which bestows upon vampires great power including immunity to the things that normally kill them. The Yathfoe-Gyuole seems to be the same thing as the Gem of Amara. A quick check did not reveal anyone in common between the two productions.
James Marsters was uncredited in the original airing of this episode, so not to spoil the surprise of Spike returning to Sunnydale. The reruns include him in the guest cast list.
In the following episode, set around Halloween 1999, Willow
mentions the party last Friday; this sets the party on the night of October 22, 1999.
Spike: I love Syphilis more than you.
Syphilis is a cronic infectious disease that is transmitted primarily by sexual intercourse.
The disease is generally characterized by skin lesions and ulcerous skin eruptions. If untreated it can cause widespread damage to the heart, brain, eyes, nervous system, bones, and joints. Late stages of syphilis can result in mental illness, blindness, severe damage to the heart and aorta, and death.
Xander: Really? You know, if I'm in the checkout lane at the Wal-Mart I've had the same one.
Wal-Mart Stores, Inc. is a worldwide chain of retail stores founded by Sam Walton in 1962. Based on revenue, Wal-Mart is the largest retailer and largest company in the world. It is also the largest private employer in the United States, Mexico and Canada. $8.90 out of every $100 spent in U.S. retail stores is spent at Wal-Mart.
Harmony: Is Antonio Banderas a vampire?
Antonio Banderas is a Spanish born actor who is considered to be quite the hunk. He also played the vampire Armand in the 1994 film Interview with the Vampire. Presumably this is why Harmony is asking the question.
Spike: Do Melanie and the kids too.
Continuing with the idea of turning Antonio Banderas into a vampire, Spike is suggesting that Harmony also bite Melanie Griffith (Antonio's wife) and their children.
Giles: It's the vampire equivalent of the Holy Grail.
Legend has it that the Holy Grail is the cup that Jesus drank from during the Last Supper, and that it was also used to catch some of his blood when he was dying on the cross. This cup became an object of great reverence, but was lost in the very early days of the Christian Church. For centuries people have spent lifetimes searching for the Grail including, most famously, the knights of King Arthur's round table. The term "Grail" or "Holy Grail" are now used to mean something that is searched for but is not real or, at least, is never found.